diff --git a/examples/gatsby-hot-reload/.dockerignore b/examples/gatsby-hot-reload/.dockerignore
index 09667e36f8..4b2a80e208 100644
--- a/examples/gatsby-hot-reload/.dockerignore
+++ b/examples/gatsby-hot-reload/.dockerignore
@@ -1,3 +1,3 @@
 node_modules
-garden.yaml
+garden.yml
 .git
diff --git a/garden-service/src/commands/base.ts b/garden-service/src/commands/base.ts
index ae3bed601b..04f632c12b 100644
--- a/garden-service/src/commands/base.ts
+++ b/garden-service/src/commands/base.ts
@@ -7,7 +7,7 @@
  */
 
 import Joi = require("joi")
-import { GardenError, RuntimeError, InternalError } from "../exceptions"
+import { GardenError, RuntimeError, InternalError, ParameterError } from "../exceptions"
 import { TaskResults } from "../task-graph"
 import { LoggerType } from "../logger/logger"
 import { ProcessResults } from "../process"
@@ -16,8 +16,6 @@ import { LogEntry } from "../logger/log-entry"
 import { printFooter } from "../logger/util"
 import { GlobalOptions } from "../cli/cli"
 
-export class ValidationError extends Error { }
-
 export interface ParameterConstructor<T> {
   help: string,
   required?: boolean,
@@ -139,7 +137,10 @@ export class IntegerParameter extends Parameter<number> {
     try {
       return parseInt(input, 10)
     } catch {
-      throw new ValidationError(`Could not parse "${input}" as integer`)
+      throw new ParameterError(`Could not parse "${input}" as integer`, {
+        expectedType: "integer",
+        input,
+      })
     }
   }
 }
@@ -164,7 +165,10 @@ export class ChoicesParameter extends Parameter<string> {
     if (this.choices.includes(input)) {
       return input
     } else {
-      throw new ValidationError(`"${input}" is not a valid argument`)
+      throw new ParameterError(`"${input}" is not a valid argument`, {
+        expectedType: `One of: ${this.choices.join(", ")}`,
+        input,
+      })
     }
   }
 
diff --git a/garden-service/src/commands/get/get-debug-info.ts b/garden-service/src/commands/get/get-debug-info.ts
index dbbe62212e..49902cf010 100644
--- a/garden-service/src/commands/get/get-debug-info.ts
+++ b/garden-service/src/commands/get/get-debug-info.ts
@@ -16,15 +16,12 @@ import { findProjectConfig } from "../../config/base"
 import { ensureDir, copy, remove, pathExists, writeFile } from "fs-extra"
 import { getPackageVersion } from "../../util/util"
 import { platform, release } from "os"
-import { join, relative } from "path"
+import { join, relative, basename } from "path"
 import execa = require("execa")
 import { LogEntry } from "../../logger/log-entry"
 import { deline } from "../../util/string"
-import { getModulesPathsFromPath } from "../../util/fs"
-import {
-  CONFIG_FILENAME,
-  ERROR_LOG_FILENAME,
-} from "../../constants"
+import { getModulesPathsFromPath, getConfigFilePath } from "../../util/fs"
+import { ERROR_LOG_FILENAME } from "../../constants"
 import dedent = require("dedent")
 import { Garden } from "../../garden"
 import { zipFolder } from "../../util/archive"
@@ -61,7 +58,9 @@ export async function collectBasicDebugInfo(root: string, gardenDirPath: string,
   await ensureDir(tempPath)
 
   // Copy project definition in tmp folder
-  await copy(join(root, CONFIG_FILENAME), join(tempPath, CONFIG_FILENAME))
+  const projectConfigFilePath = await getConfigFilePath(root)
+  const projectConfigFilename = basename(projectConfigFilePath)
+  await copy(projectConfigFilePath, join(tempPath, projectConfigFilename))
   // Check if error logs exist and copy it over if it does
   if (await pathExists(join(root, ERROR_LOG_FILENAME))) {
     await copy(join(root, ERROR_LOG_FILENAME), join(tempPath, ERROR_LOG_FILENAME))
@@ -74,7 +73,9 @@ export async function collectBasicDebugInfo(root: string, gardenDirPath: string,
   for (const servicePath of paths) {
     const tempServicePath = join(tempPath, relative(root, servicePath))
     await ensureDir(tempServicePath)
-    await copy(join(servicePath, CONFIG_FILENAME), join(tempServicePath, CONFIG_FILENAME))
+    const moduleConfigFilePath = await getConfigFilePath(servicePath)
+    const moduleConfigFilename = basename(moduleConfigFilePath)
+    await copy(moduleConfigFilePath, join(tempServicePath, moduleConfigFilename))
 
     // Check if error logs exist and copy them over if they do
     if (await pathExists(join(servicePath, ERROR_LOG_FILENAME))) {
diff --git a/garden-service/src/config/base.ts b/garden-service/src/config/base.ts
index 49bf9ac4fd..390e586809 100644
--- a/garden-service/src/config/base.ts
+++ b/garden-service/src/config/base.ts
@@ -6,14 +6,15 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-import { join, sep, resolve, relative } from "path"
+import { sep, resolve, relative, basename } from "path"
 import * as yaml from "js-yaml"
 import { readFile } from "fs-extra"
 import { omit, flatten, isPlainObject, find } from "lodash"
 import { baseModuleSpecSchema, ModuleResource } from "./module"
 import { ConfigurationError } from "../exceptions"
-import { CONFIG_FILENAME, DEFAULT_API_VERSION } from "../constants"
+import { DEFAULT_API_VERSION } from "../constants"
 import { ProjectResource } from "../config/project"
+import { getConfigFilePath } from "../util/fs"
 
 export interface GardenResource {
   apiVersion: string
@@ -26,7 +27,7 @@ const baseModuleSchemaKeys = Object.keys(baseModuleSpecSchema.describe().childre
 
 export async function loadConfig(projectRoot: string, path: string): Promise<GardenResource[]> {
   // TODO: nicer error messages when load/validation fails
-  const absPath = join(path, CONFIG_FILENAME)
+  const absPath = await getConfigFilePath(path)
   let fileData: Buffer
   let rawSpecs: any[]
 
@@ -40,7 +41,7 @@ export async function loadConfig(projectRoot: string, path: string): Promise<Gar
   try {
     rawSpecs = yaml.safeLoadAll(fileData.toString()) || []
   } catch (err) {
-    throw new ConfigurationError(`Could not parse ${CONFIG_FILENAME} in directory ${path} as valid YAML`, err)
+    throw new ConfigurationError(`Could not parse ${basename(absPath)} in directory ${path} as valid YAML`, err)
   }
 
   const resources: GardenResource[] = flatten(rawSpecs.map(s => prepareResources(s, path, projectRoot)))
diff --git a/garden-service/src/constants.ts b/garden-service/src/constants.ts
index d10989d07c..6200c0c14a 100644
--- a/garden-service/src/constants.ts
+++ b/garden-service/src/constants.ts
@@ -10,7 +10,6 @@ import { resolve, join } from "path"
 
 export const isPkg = !!(<any>process).pkg
 
-export const CONFIG_FILENAME = "garden.yml"
 export const LOCAL_CONFIG_FILENAME = "local-config.yml"
 export const GARDEN_SERVICE_ROOT = isPkg ? resolve(process.execPath, "..") : resolve(__dirname, "..", "..")
 export const STATIC_DIR = join(GARDEN_SERVICE_ROOT, "static")
diff --git a/garden-service/src/garden.ts b/garden-service/src/garden.ts
index bb67e1a904..f28bda3c0e 100644
--- a/garden-service/src/garden.ts
+++ b/garden-service/src/garden.ts
@@ -7,7 +7,7 @@
  */
 
 import Bluebird = require("bluebird")
-import { parse, relative, resolve, sep, join } from "path"
+import { parse, relative, resolve, sep } from "path"
 import { flatten, isString, cloneDeep, sortBy, set, zip } from "lodash"
 const AsyncLock = require("async-lock")
 
@@ -35,12 +35,12 @@ import { BuildDependencyConfig, ModuleConfig, baseModuleSpecSchema, ModuleResour
 import { ModuleConfigContext, ContextResolveOpts } from "./config/config-context"
 import { createPluginContext } from "./plugin-context"
 import { ModuleAndRuntimeActions, Plugins, RegisterPluginParam } from "./types/plugin/plugin"
-import { SUPPORTED_PLATFORMS, SupportedPlatform, CONFIG_FILENAME, DEFAULT_GARDEN_DIR_NAME } from "./constants"
+import { SUPPORTED_PLATFORMS, SupportedPlatform, DEFAULT_GARDEN_DIR_NAME } from "./constants"
 import { platform, arch } from "os"
 import { LogEntry } from "./logger/log-entry"
 import { EventBus } from "./events"
 import { Watcher } from "./watch"
-import { getIgnorer, Ignorer, getModulesPathsFromPath } from "./util/fs"
+import { getIgnorer, Ignorer, getModulesPathsFromPath, getConfigFilePath } from "./util/fs"
 import { Provider, ProviderConfig, getProviderDependencies } from "./config/provider"
 import { ResolveProviderTask } from "./tasks/resolve-provider"
 import { ActionHelper } from "./actions"
@@ -407,13 +407,13 @@ export class Garden {
 
       this.resolvedProviders = Object.values(taskResults).map(result => result.output)
 
-      for (const provider of this.resolvedProviders) {
-        for (const moduleConfig of provider.moduleConfigs) {
+      await Bluebird.map(this.resolvedProviders, async (provider) =>
+        Bluebird.map(provider.moduleConfigs, async (moduleConfig) => {
           // Make sure module and all nested entities are scoped to the plugin
           moduleConfig.plugin = provider.name
-          this.addModule(moduleConfig)
-        }
-      }
+          return this.addModule(moduleConfig)
+        }),
+      )
     })
 
     return this.resolvedProviders
@@ -622,9 +622,7 @@ export class Garden {
         }
       })
 
-      for (const config of rawConfigs) {
-        this.addModule(config)
-      }
+      await Bluebird.map(rawConfigs, async (config) => this.addModule(config))
 
       this.modulesScanned = true
     })
@@ -641,14 +639,14 @@ export class Garden {
    * Add a module config to the context, after validating and calling the appropriate configure plugin handler.
    * Template strings should be resolved on the config before calling this.
    */
-  private addModule(config: ModuleConfig) {
+  private async addModule(config: ModuleConfig) {
     const key = getModuleKey(config.name, config.plugin)
 
     if (this.moduleConfigs[key]) {
-      const [pathA, pathB] = [
-        relative(this.projectRoot, join(this.moduleConfigs[key].path, CONFIG_FILENAME)),
-        relative(this.projectRoot, join(config.path, CONFIG_FILENAME)),
-      ].sort()
+      const paths = [this.moduleConfigs[key].path, config.path]
+      const [pathA, pathB] = (await Bluebird
+        .map(paths, async (path) => relative(this.projectRoot, await getConfigFilePath(path))))
+        .sort()
 
       throw new ConfigurationError(
         `Module ${key} is declared multiple times (in '${pathA}' and '${pathB}')`,
diff --git a/garden-service/src/types/module.ts b/garden-service/src/types/module.ts
index 4f0d52b5cb..a3d4d38f73 100644
--- a/garden-service/src/types/module.ts
+++ b/garden-service/src/types/module.ts
@@ -6,7 +6,6 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/.
  */
 
-import { resolve } from "path"
 import { flatten, uniq, cloneDeep, keyBy } from "lodash"
 import { getNames } from "../util/util"
 import { TestSpec } from "../config/test"
@@ -20,7 +19,7 @@ import * as Joi from "joi"
 import { joiArray, joiIdentifier, joiIdentifierMap } from "../config/common"
 import { ConfigGraph } from "../config-graph"
 import * as Bluebird from "bluebird"
-import { CONFIG_FILENAME } from "../constants"
+import { getConfigFilePath } from "../util/fs"
 
 export interface FileCopySpec {
   source: string
@@ -96,7 +95,7 @@ export interface ModuleConfigMap<T extends ModuleConfig = ModuleConfig> {
 }
 
 export async function moduleFromConfig(garden: Garden, graph: ConfigGraph, config: ModuleConfig): Promise<Module> {
-  const configPath = resolve(config.path, CONFIG_FILENAME)
+  const configPath = await getConfigFilePath(config.path)
   const version = await garden.resolveVersion(config.name, config.build.dependencies)
 
   // Always include configuration file
diff --git a/garden-service/src/util/fs.ts b/garden-service/src/util/fs.ts
index 4ce313ae3d..35b2e64ae2 100644
--- a/garden-service/src/util/fs.ts
+++ b/garden-service/src/util/fs.ts
@@ -9,13 +9,16 @@
 import klaw = require("klaw")
 import * as _spawn from "cross-spawn"
 import { pathExists, readFile } from "fs-extra"
+import * as Bluebird from "bluebird"
 import minimatch = require("minimatch")
 import { some } from "lodash"
 import { join, basename, win32, posix, relative, parse } from "path"
-import { CONFIG_FILENAME } from "../constants"
+import { ValidationError } from "../exceptions"
 // NOTE: Importing from ignore/ignore doesn't work on Windows
 const ignore = require("ignore")
 
+const VALID_CONFIG_FILENAMES = ["garden.yml", "garden.yaml"]
+
 /*
   Warning: Don't make any async calls in the loop body when using this function, since this may cause
   funky concurrency behavior.
@@ -50,6 +53,40 @@ export async function* scanDirectory(path: string, opts?: klaw.Options): AsyncIt
   }
 }
 
+/**
+ * Returns the expected full path to the Garden config filename.
+ *
+ * If a valid config filename is found at the given path, it returns the full path to it.
+ * If no config file is found, it returns the path joined with the first value from the VALID_CONFIG_FILENAMES list.
+ * (The check for whether or not a project or a module has a valid config file at all is handled elsewehere.)
+ *
+ * Throws an error if there are more than one valid config filenames at the given path.
+ */
+export async function getConfigFilePath(path: string) {
+  const configFilePaths = await Bluebird
+    .map(VALID_CONFIG_FILENAMES, async (filename) => {
+      const configFilePath = join(path, filename)
+      return (await pathExists(configFilePath)) ? configFilePath : undefined
+    })
+    .filter(Boolean)
+
+  if (configFilePaths.length > 1) {
+    throw new ValidationError(`Found more than one Garden config file at ${path}.`, {
+      path,
+      configFilenames: configFilePaths.map(filePath => basename(filePath || "")).join(", "),
+    })
+  }
+
+  return configFilePaths[0] || join(path, VALID_CONFIG_FILENAMES[0])
+}
+
+/**
+ * Helper function to check whether a given filename is a valid Garden config filename
+ */
+export function isConfigFilename(filename: string) {
+  return VALID_CONFIG_FILENAMES.includes(filename)
+}
+
 export async function getChildDirNames(parentDir: string): Promise<string[]> {
   let dirNames: string[] = []
   // Filter on hidden dirs by default. We could make the filter function a param if needed later
@@ -125,7 +162,7 @@ export async function getModulesPathsFromPath(dir: string, gardenDirPath: string
 
     const parsedPath = parse(item.path)
 
-    if (parsedPath.base !== CONFIG_FILENAME) {
+    if (!isConfigFilename(parsedPath.base)) {
       continue
     }
 
diff --git a/garden-service/src/watch.ts b/garden-service/src/watch.ts
index 18e0d394b6..22ce066a26 100644
--- a/garden-service/src/watch.ts
+++ b/garden-service/src/watch.ts
@@ -10,13 +10,13 @@ import { watch, FSWatcher } from "chokidar"
 import { parse, relative } from "path"
 import { pathToCacheContext } from "./cache"
 import { Module } from "./types/module"
-import { CONFIG_FILENAME } from "./constants"
 import { Garden } from "./garden"
 import { LogEntry } from "./logger/log-entry"
 import * as klaw from "klaw"
 import { registerCleanupFunction } from "./util/util"
 import * as Bluebird from "bluebird"
 import { some } from "lodash"
+import { isConfigFilename } from "./util/fs"
 
 export type ChangeHandler = (module: Module | null, configChanged: boolean) => Promise<void>
 
@@ -117,12 +117,12 @@ export class Watcher {
     const parsed = parse(path)
     const filename = parsed.base
 
-    if (filename === CONFIG_FILENAME || filename === ".gitignore" || filename === ".gardenignore") {
+    if (isConfigFilename(filename) || filename === ".gitignore" || filename === ".gardenignore") {
       this.invalidateCached(modules)
 
       if (changedModuleNames.length > 0) {
         this.garden.events.emit("moduleConfigChanged", { names: changedModuleNames, path })
-      } else if (filename === CONFIG_FILENAME) {
+      } else if (isConfigFilename(filename)) {
         if (parsed.dir === this.garden.projectRoot) {
           this.garden.events.emit("projectConfigChanged", {})
         } else {
@@ -160,7 +160,7 @@ export class Watcher {
       klaw(path, scanOpts)
         .on("data", (item) => {
           const parsed = parse(item.path)
-          if (item.path !== path && parsed.base === CONFIG_FILENAME) {
+          if (item.path !== path && isConfigFilename(parsed.base)) {
             configChanged = true
             this.garden.events.emit("configAdded", { path: item.path })
           }
diff --git a/garden-service/test/helpers.ts b/garden-service/test/helpers.ts
index 8869944bbb..056ed8de84 100644
--- a/garden-service/test/helpers.ts
+++ b/garden-service/test/helpers.ts
@@ -26,7 +26,7 @@ import { Garden, GardenOpts } from "../src/garden"
 import { ModuleConfig } from "../src/config/module"
 import { mapValues, fromPairs } from "lodash"
 import { ModuleVersion } from "../src/vcs/vcs"
-import { CONFIG_FILENAME, GARDEN_SERVICE_ROOT } from "../src/constants"
+import { GARDEN_SERVICE_ROOT } from "../src/constants"
 import { EventBus, Events } from "../src/events"
 import { ValueOf } from "../src/util/util"
 import { Ignorer } from "../src/util/fs"
@@ -400,7 +400,10 @@ export function stubExtSources(garden: Garden) {
 }
 
 export function getExampleProjects() {
-  const names = readdirSync(examplesDir).filter(n => existsSync(join(examplesDir, n, CONFIG_FILENAME)))
+  const names = readdirSync(examplesDir).filter(n => {
+    const basePath = join(examplesDir, n)
+    return existsSync(join(basePath, "garden.yml")) || existsSync(join(basePath, "garden.yaml"))
+  })
   return fromPairs(names.map(n => [n, join(examplesDir, n)]))
 }
 
diff --git a/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yaml b/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yaml
new file mode 100644
index 0000000000..bd1f17723f
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yaml
@@ -0,0 +1,11 @@
+project:
+  name: test-project-a
+  environmentDefaults:
+    variables:
+      some: variable
+  environments:
+    - name: local
+      providers:
+        - name: test-plugin
+        - name: test-plugin-b
+    - name: other
diff --git a/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yml b/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yml
new file mode 100644
index 0000000000..bd1f17723f
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-duplicate-yaml-file-extensions/garden.yml
@@ -0,0 +1,11 @@
+project:
+  name: test-project-a
+  environmentDefaults:
+    variables:
+      some: variable
+  environments:
+    - name: local
+      providers:
+        - name: test-plugin
+        - name: test-plugin-b
+    - name: other
diff --git a/garden-service/test/unit/data/test-project-yaml-file-extensions/garden.yaml b/garden-service/test/unit/data/test-project-yaml-file-extensions/garden.yaml
new file mode 100644
index 0000000000..bd1f17723f
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-yaml-file-extensions/garden.yaml
@@ -0,0 +1,11 @@
+project:
+  name: test-project-a
+  environmentDefaults:
+    variables:
+      some: variable
+  environments:
+    - name: local
+      providers:
+        - name: test-plugin
+        - name: test-plugin-b
+    - name: other
diff --git a/garden-service/test/unit/data/test-project-yaml-file-extensions/module-no-config/foo.yml b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-no-config/foo.yml
new file mode 100644
index 0000000000..d1ed9c6757
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-no-config/foo.yml
@@ -0,0 +1,3 @@
+module:
+  name: module-foo
+  type: test
\ No newline at end of file
diff --git a/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yaml/garden.yaml b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yaml/garden.yaml
new file mode 100644
index 0000000000..8168b8bcbd
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yaml/garden.yaml
@@ -0,0 +1,3 @@
+module:
+  name: module-yaml
+  type: test
diff --git a/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yml/garden.yml b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yml/garden.yml
new file mode 100644
index 0000000000..a3f8fa94c7
--- /dev/null
+++ b/garden-service/test/unit/data/test-project-yaml-file-extensions/module-yml/garden.yml
@@ -0,0 +1,3 @@
+module:
+  name: module-yml
+  type: test
diff --git a/garden-service/test/unit/src/build-dir.ts b/garden-service/test/unit/src/build-dir.ts
index cb414b0f2c..4389e56ff3 100644
--- a/garden-service/test/unit/src/build-dir.ts
+++ b/garden-service/test/unit/src/build-dir.ts
@@ -4,7 +4,7 @@ import { pathExists, readdir } from "fs-extra"
 import { expect } from "chai"
 import { BuildTask } from "../../../src/tasks/build"
 import { makeTestGarden, dataDir } from "../../helpers"
-import { CONFIG_FILENAME } from "../../../src/constants"
+import { getConfigFilePath } from "../../../src/util/fs"
 
 /*
   Module dependency diagram for test-project-build-products
@@ -52,7 +52,7 @@ describe("BuildDir", () => {
     const buildDirA = await garden.buildDir.buildPath(moduleA.name)
 
     const copiedPaths = [
-      join(buildDirA, CONFIG_FILENAME),
+      await getConfigFilePath(buildDirA),
       join(buildDirA, "some-dir", "some-file"),
     ]
 
diff --git a/garden-service/test/unit/src/commands/get/get-debug-info.ts b/garden-service/test/unit/src/commands/get/get-debug-info.ts
index 4a9d8dbf02..8fc8c199ed 100644
--- a/garden-service/test/unit/src/commands/get/get-debug-info.ts
+++ b/garden-service/test/unit/src/commands/get/get-debug-info.ts
@@ -19,10 +19,11 @@ import {
   GetDebugInfoCommand,
 } from "../../../../../src/commands/get/get-debug-info"
 import { readdirSync, remove, pathExists, readJSONSync } from "fs-extra"
-import { CONFIG_FILENAME, ERROR_LOG_FILENAME } from "../../../../../src/constants"
+import { ERROR_LOG_FILENAME } from "../../../../../src/constants"
 import { join, relative } from "path"
 import { Garden } from "../../../../../src/garden"
 import { LogEntry } from "../../../../../src/logger/log-entry"
+import { getConfigFilePath } from "../../../../../src/util/fs"
 
 const debugZipFileRegex = new RegExp(/debug-info-.*?.zip/)
 
@@ -98,7 +99,7 @@ describe("GetDebugInfoCommand", () => {
       await collectBasicDebugInfo(garden.projectRoot, garden.gardenDirPath, log)
 
       // we first check if the main garden.yml exists
-      expect(await pathExists(join(gardenDebugTmp, CONFIG_FILENAME))).to.equal(true)
+      expect(await pathExists(await getConfigFilePath(gardenDebugTmp))).to.equal(true)
       const graph = await garden.getConfigGraph()
 
       // Check that each module config files have been copied over and
@@ -110,7 +111,7 @@ describe("GetDebugInfoCommand", () => {
         expect(await pathExists(join(gardenDebugTmp, moduleRelativePath))).to.equal(true)
 
         // Checks config file is copied over
-        expect(await pathExists(join(gardenDebugTmp, moduleRelativePath, CONFIG_FILENAME))).to.equal(true)
+        expect(await pathExists(await getConfigFilePath(join(gardenDebugTmp, moduleRelativePath)))).to.equal(true)
 
         // Checks error logs are copied over if they exist
         if (await pathExists(join(module.path, ERROR_LOG_FILENAME))) {
diff --git a/garden-service/test/unit/src/garden.ts b/garden-service/test/unit/src/garden.ts
index aa9fbb8c79..788ff7faaa 100644
--- a/garden-service/test/unit/src/garden.ts
+++ b/garden-service/test/unit/src/garden.ts
@@ -51,6 +51,16 @@ describe("Garden", () => {
       expect(garden).to.be.ok
     })
 
+    it("should initialize a project with config files with yaml and yml extensions", async () => {
+      const garden = await makeTestGarden(getDataDir("test-project-yaml-file-extensions"))
+      expect(garden).to.be.ok
+    })
+
+    it("should throw if a project has config files with yaml and yml extensions in the same dir", async () => {
+      const path = getDataDir("test-project-duplicate-yaml-file-extensions")
+      await expectError(async () => makeTestGarden(path), "validation")
+    })
+
     it("should parse and resolve the config from the project root", async () => {
       const garden = await makeTestGardenA()
       const projectRoot = garden.projectRoot
@@ -688,6 +698,12 @@ describe("Garden", () => {
         ),
       )
     })
+
+    it("should scan and add modules with config files with yaml and yml extensions", async () => {
+      const garden = await makeTestGarden(getDataDir("test-project-yaml-file-extensions"))
+      const modules = await garden.resolveModuleConfigs()
+      expect(getNames(modules).sort()).to.eql(["module-yaml", "module-yml"])
+    })
   })
 
   describe("loadModuleConfigs", () => {
diff --git a/garden-service/test/unit/src/util/fs.ts b/garden-service/test/unit/src/util/fs.ts
index 80b41dd78e..9777f715b9 100644
--- a/garden-service/test/unit/src/util/fs.ts
+++ b/garden-service/test/unit/src/util/fs.ts
@@ -1,7 +1,16 @@
 import { expect } from "chai"
-import { join } from "path"
-import { getDataDir } from "../../../helpers"
-import { scanDirectory, toCygwinPath, getChildDirNames } from "../../../../src/util/fs"
+import { join, basename } from "path"
+import { getDataDir, expectError } from "../../../helpers"
+import {
+  scanDirectory,
+  toCygwinPath,
+  getChildDirNames,
+  isConfigFilename,
+  getConfigFilePath,
+} from "../../../../src/util/fs"
+
+const projectYamlFileExtensions = getDataDir("test-project-yaml-file-extensions")
+const projectDuplicateYamlFileExtensions = getDataDir("test-project-duplicate-yaml-file-extensions")
 
 describe("util", () => {
   describe("scanDirectory", () => {
@@ -53,4 +62,42 @@ describe("util", () => {
       expect(toCygwinPath(path)).to.equal("/cygdrive/c/some/path/")
     })
   })
+
+  describe("getConfigFilePath", () => {
+    context("name of the file is garden.yml", () => {
+      it("should return the full path to the config file", async () => {
+        const testPath = join(projectYamlFileExtensions, "module-yml")
+        expect(await getConfigFilePath(testPath)).to.eql(join(testPath, "garden.yml"))
+      })
+    })
+    context("name of the file is garden.yaml", () => {
+      it("should return the full path to the config file", async () => {
+        const testPath = join(projectYamlFileExtensions, "module-yml")
+        expect(await getConfigFilePath(testPath)).to.eql(join(testPath, "garden.yml"))
+      })
+    })
+    it("should throw if multiple valid config files found at the given path", async () => {
+      await expectError(() => getConfigFilePath(projectDuplicateYamlFileExtensions), "validation")
+    })
+    it("should return a valid default path if no config file found at the given path", async () => {
+      const testPath = join(projectYamlFileExtensions, "module-no-config")
+      const result = await getConfigFilePath(testPath)
+      expect(isConfigFilename(basename(result))).to.be.true
+    })
+  })
+
+  describe("isConfigFilename", () => {
+    it("should return true if the name of the file is garden.yaml", async () => {
+      expect(await isConfigFilename("garden.yaml")).to.be.true
+    })
+    it("should return true if the name of the file is garden.yml", async () => {
+      expect(await isConfigFilename("garden.yml")).to.be.true
+    })
+    it("should return false otherwise", async () => {
+      const badNames = ["agarden.yml", "garden.ymla", "garden.yaaml", "garden.ml"]
+      for (const name of badNames) {
+        expect(isConfigFilename(name)).to.be.false
+      }
+    })
+  })
 })
diff --git a/garden-service/test/unit/src/watch.ts b/garden-service/test/unit/src/watch.ts
index 60097e4b4b..dc4406273e 100644
--- a/garden-service/test/unit/src/watch.ts
+++ b/garden-service/test/unit/src/watch.ts
@@ -1,10 +1,10 @@
-import { resolve } from "path"
+import { resolve, join } from "path"
 import { TestGarden, dataDir, makeTestGarden } from "../../helpers"
 import { expect } from "chai"
 import { CacheContext, pathToCacheContext } from "../../../src/cache"
-import { CONFIG_FILENAME } from "../../../src/constants"
 import pEvent = require("p-event")
 import { createFile, remove, pathExists } from "fs-extra"
+import { getConfigFilePath } from "../../../src/util/fs"
 
 describe("Watcher", () => {
   let garden: TestGarden
@@ -39,7 +39,7 @@ describe("Watcher", () => {
   }
 
   it("should emit a moduleConfigChanged changed event when module config is changed", async () => {
-    const path = resolve(modulePath, CONFIG_FILENAME)
+    const path = await getConfigFilePath(modulePath)
     emitEvent("change", path)
     expect(garden.events.eventLog).to.eql([
       { name: "moduleConfigChanged", payload: { names: ["module-a"], path } },
@@ -47,7 +47,7 @@ describe("Watcher", () => {
   })
 
   it("should emit a moduleConfigChanged event when module config is changed and include field is set", async () => {
-    const path = resolve(includeModulePath, CONFIG_FILENAME)
+    const path = await getConfigFilePath(includeModulePath)
     emitEvent("change", path)
     expect(garden.events.eventLog).to.eql([
       { name: "moduleConfigChanged", payload: { names: ["with-include"], path } },
@@ -55,37 +55,41 @@ describe("Watcher", () => {
   })
 
   it("should clear all module caches when a module config is changed", async () => {
-    emitEvent("change", resolve(modulePath, CONFIG_FILENAME))
+    const path = await getConfigFilePath(modulePath)
+    emitEvent("change", path)
     expect(garden.cache.getByContext(moduleContext)).to.eql(new Map())
   })
 
   it("should emit a projectConfigChanged changed event when project config is changed", async () => {
-    emitEvent("change", resolve(garden.projectRoot, CONFIG_FILENAME))
+    const path = await getConfigFilePath(garden.projectRoot)
+    emitEvent("change", path)
     expect(garden.events.eventLog).to.eql([
       { name: "projectConfigChanged", payload: {} },
     ])
   })
 
   it("should emit a projectConfigChanged changed event when project config is removed", async () => {
-    emitEvent("unlink", resolve(garden.projectRoot, CONFIG_FILENAME))
+    const path = await getConfigFilePath(garden.projectRoot)
+    emitEvent("unlink", path)
     expect(garden.events.eventLog).to.eql([
       { name: "projectConfigChanged", payload: {} },
     ])
   })
 
   it("should clear all module caches when project config is changed", async () => {
-    emitEvent("change", resolve(garden.projectRoot, CONFIG_FILENAME))
+    const path = await getConfigFilePath(garden.projectRoot)
+    emitEvent("change", path)
     expect(garden.cache.getByContext(moduleContext)).to.eql(new Map())
   })
 
   it("should emit a configAdded event when adding a garden.yml file", async () => {
-    const path = resolve(garden.projectRoot, "module-b", CONFIG_FILENAME)
+    const path = await getConfigFilePath(join(garden.projectRoot, "module-b"))
     emitEvent("add", path)
     expect(await waitForEvent("configAdded")).to.eql({ path })
   })
 
   it("should emit a configRemoved event when removing a garden.yml file", async () => {
-    const path = resolve(garden.projectRoot, "module-b", CONFIG_FILENAME)
+    const path = await getConfigFilePath(join(garden.projectRoot, "module-b"))
     emitEvent("unlink", path)
     expect(garden.events.eventLog).to.eql([
       { name: "configRemoved", payload: { path } },
@@ -155,7 +159,7 @@ describe("Watcher", () => {
   it("should emit a configAdded event when a directory is added that contains a garden.yml file", async () => {
     emitEvent("addDir", modulePath)
     expect(await waitForEvent("configAdded")).to.eql({
-      path: resolve(modulePath, CONFIG_FILENAME),
+      path: await getConfigFilePath(modulePath),
     })
   })