diff --git a/apps/heft/src/plugins/SassTypingsPlugin/SassTypingsGenerator.ts b/apps/heft/src/plugins/SassTypingsPlugin/SassTypingsGenerator.ts
index 3ba513ca9e2..8ba7510cd8c 100644
--- a/apps/heft/src/plugins/SassTypingsPlugin/SassTypingsGenerator.ts
+++ b/apps/heft/src/plugins/SassTypingsPlugin/SassTypingsGenerator.ts
@@ -143,6 +143,12 @@ export class SassTypingsGenerator extends StringValuesTypingsGenerator {
       indentedSyntax: path.extname(filePath).toLowerCase() === '.sass'
     });
 
+    // Register any @import files as dependencies.
+    const target: string = result.stats.entry;
+    for (const dependency of result.stats.includedFiles) {
+      this.registerDependency(target, dependency);
+    }
+
     return result.css.toString();
   }
 
diff --git a/common/changes/@rushstack/heft/halfnibble-typings-dep-maps_2020-11-11-06-09.json b/common/changes/@rushstack/heft/halfnibble-typings-dep-maps_2020-11-11-06-09.json
new file mode 100644
index 00000000000..2d040b18af3
--- /dev/null
+++ b/common/changes/@rushstack/heft/halfnibble-typings-dep-maps_2020-11-11-06-09.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/heft",
+      "comment": "Update Sass typings generation to update in watch mode when a dependency changes.",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@rushstack/heft",
+  "email": "halfnibble@users.noreply.github.com"
+}
\ No newline at end of file
diff --git a/common/changes/@rushstack/typings-generator/halfnibble-typings-dep-maps_2020-11-11-06-09.json b/common/changes/@rushstack/typings-generator/halfnibble-typings-dep-maps_2020-11-11-06-09.json
new file mode 100644
index 00000000000..81acd92494e
--- /dev/null
+++ b/common/changes/@rushstack/typings-generator/halfnibble-typings-dep-maps_2020-11-11-06-09.json
@@ -0,0 +1,11 @@
+{
+  "changes": [
+    {
+      "packageName": "@rushstack/typings-generator",
+      "comment": "Add register dependency feature for typings generation. ",
+      "type": "patch"
+    }
+  ],
+  "packageName": "@rushstack/typings-generator",
+  "email": "halfnibble@users.noreply.github.com"
+}
\ No newline at end of file
diff --git a/common/reviews/api/typings-generator.api.md b/common/reviews/api/typings-generator.api.md
index c0383146a83..67feec96ead 100644
--- a/common/reviews/api/typings-generator.api.md
+++ b/common/reviews/api/typings-generator.api.md
@@ -54,6 +54,7 @@ export class TypingsGenerator {
     generateTypingsAsync(): Promise<void>;
     // (undocumented)
     protected _options: ITypingsGeneratorOptions;
+    registerDependency(target: string, dependency: string): void;
     // (undocumented)
     runWatcherAsync(): Promise<void>;
 }
diff --git a/libraries/typings-generator/src/TypingsGenerator.ts b/libraries/typings-generator/src/TypingsGenerator.ts
index 988ab88d586..45f2a2702e2 100644
--- a/libraries/typings-generator/src/TypingsGenerator.ts
+++ b/libraries/typings-generator/src/TypingsGenerator.ts
@@ -34,6 +34,12 @@ export interface ITypingsGeneratorOptions<TTypingsResult = string | undefined> {
  * @public
  */
 export class TypingsGenerator {
+  // Map of target file path -> Set<dependency file path>
+  private _targetMap: Map<string, Set<string>>;
+
+  // Map of dependency file path -> Set<target file path>
+  private _dependencyMap: Map<string, Set<string>>;
+
   protected _options: ITypingsGeneratorOptions;
 
   public constructor(options: ITypingsGeneratorOptions) {
@@ -70,6 +76,10 @@ export class TypingsGenerator {
     }
 
     this._options.fileExtensions = this._normalizeFileExtensions(this._options.fileExtensions);
+
+    this._targetMap = new Map();
+
+    this._dependencyMap = new Map();
   }
 
   public async generateTypingsAsync(): Promise<void> {
@@ -121,7 +131,37 @@ export class TypingsGenerator {
     });
   }
 
+  /**
+   * Register file dependencies that may effect the typings of a target file.
+   * Note: This feature is only useful in watch mode.
+   * The registerDependency method must be called in the body of parseAndGenerateTypings every
+   * time because the registry for a file is cleared at the beginning of processing.
+   */
+  public registerDependency(target: string, dependency: string): void {
+    let targetDependencySet: Set<string> | undefined = this._targetMap.get(target);
+    if (!targetDependencySet) {
+      targetDependencySet = new Set();
+      this._targetMap.set(target, targetDependencySet);
+    }
+    targetDependencySet.add(dependency);
+
+    let dependencyTargetSet: Set<string> | undefined = this._dependencyMap.get(dependency);
+    if (!dependencyTargetSet) {
+      dependencyTargetSet = new Set();
+      this._dependencyMap.set(dependency, dependencyTargetSet);
+    }
+    dependencyTargetSet.add(target);
+  }
+
   private async _parseFileAndGenerateTypingsAsync(locFilePath: string): Promise<void> {
+    // Clear registered dependencies prior to reprocessing.
+    this._clearDependencies(locFilePath);
+
+    // Check for targets that register this file as a dependency, and reprocess them too.
+    for (const target of this._getDependencyTargets(locFilePath)) {
+      await this._parseFileAndGenerateTypingsAsync(target);
+    }
+
     try {
       const fileContents: string = await FileSystem.readFileAsync(locFilePath);
       const typingsData: string | undefined = await this._options.parseAndGenerateTypings(
@@ -152,6 +192,20 @@ export class TypingsGenerator {
     }
   }
 
+  private _clearDependencies(target: string): void {
+    const targetDependencySet: Set<string> | undefined = this._targetMap.get(target);
+    if (targetDependencySet) {
+      for (const dependency of targetDependencySet) {
+        this._dependencyMap.get(dependency)!.delete(target);
+      }
+      targetDependencySet.clear();
+    }
+  }
+
+  private _getDependencyTargets(dependency: string): string[] {
+    return [...(this._dependencyMap.get(dependency)?.keys() || [])];
+  }
+
   private _getTypingsFilePath(locFilePath: string): string {
     return path.resolve(
       this._options.generatedTsFolder,