diff --git a/.gitignore b/.gitignore
index 2acfbbbb..d32ba5f0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,4 +7,5 @@
 .scala-build
 *.iml
 tmp
-out
\ No newline at end of file
+out
+.history
\ No newline at end of file
diff --git a/README.md b/README.md
index 72311cc1..94cb383d 100644
--- a/README.md
+++ b/README.md
@@ -96,6 +96,7 @@ ivy"io.github.iltotore::iron:version"
 | iron-cats       | ✔️  | ✔️  | ✔️     |
 | iron-circe      | ✔️  | ✔️  | ✔️     |
 | iron-ciris      | ✔️  | ✔️  | ✔️     |
+| iron-decline    | ✔️  | ✔️  | ✔️     |
 | iron-jsoniter   | ✔️  | ✔️  | ✔️     |
 | iron-scalacheck | ✔️  | ✔️  | ❌      |
 | iron-skunk      | ✔️  | ✔️  | ✔️     |
diff --git a/build.sc b/build.sc
index 3daf9f29..9f2f041d 100644
--- a/build.sc
+++ b/build.sc
@@ -77,7 +77,7 @@ object docs extends BaseModule {
 
   def artifactName = "iron-docs"
 
-  val modules: Seq[ScalaModule] = Seq(main, cats, circe, upickle, ciris, jsoniter, scalacheck, skunk, zio, zioJson)
+  val modules: Seq[ScalaModule] = Seq(main, cats, circe, decline, upickle, ciris, jsoniter, scalacheck, skunk, zio, zioJson)
 
   def docSources = T.sources {
     T.traverse(modules)(_.docSources)().flatten
@@ -140,7 +140,8 @@ object docs extends BaseModule {
     ".*zio[^\\.json].*" -> ("scaladoc3", "https://javadoc.io/doc/dev.zio/zio_3/latest/"),
     ".*org.scalacheck.*" -> ("scaladoc3", "https://javadoc.io/doc/org.scalacheck/scalacheck_3/latest/"),
     ".*org.scalacheck.*" -> ("scaladoc3", "https://javadoc.io/doc/org.scalacheck/scalacheck_3/latest/"),
-    ".*skunk.*" -> ("scaladoc3", "https://javadoc.io/doc/org.tpolecat/skunk-docs_3/latest/")
+    ".*skunk.*" -> ("scaladoc3", "https://javadoc.io/doc/org.tpolecat/skunk-docs_3/latest/"),
+    ".*com.monovore.decline.*" -> ("scaladoc3", "https://javadoc.io/doc/com.monovore/decline_3/latest/")
   )
 
   def scalaDocOptions = {
@@ -434,3 +435,18 @@ object doobie extends SubModule {
 
   object test extends Tests
 }
+
+object decline extends SubModule {
+
+  def artifactName = "iron-decline"
+
+  def ivyDeps = Agg(
+    ivy"com.monovore::decline::2.4.1"
+  )
+
+  object test extends Tests
+
+  object js extends JSCrossModule
+
+  object native extends NativeCrossModule
+}
diff --git a/decline/src/io/github/iltotore/iron/decline.scala b/decline/src/io/github/iltotore/iron/decline.scala
new file mode 100644
index 00000000..0911d526
--- /dev/null
+++ b/decline/src/io/github/iltotore/iron/decline.scala
@@ -0,0 +1,23 @@
+package io.github.iltotore.iron
+
+import _root_.com.monovore.decline.Argument
+import _root_.io.github.iltotore.iron.*
+import cats.data.Validated
+import cats.data.Validated.Valid
+import cats.data.Validated.Invalid
+import cats.data.ValidatedNel // Add this import
+
+object decline:
+  inline given [A, B](using inline argument: Argument[A], inline constraint: Constraint[A, B]): Argument[A :| B] =
+    new Argument[A :| B]:
+      def read(string: String): ValidatedNel[String, A :| B] =
+        argument.read(string) match
+          case Valid(a) => a.refineEither[B] match
+            case Left(value) => Validated.invalidNel(value)
+            case Right(value) => Validated.validNel(value)
+          case Invalid(e) => Validated.invalid(e)
+
+      def defaultMetavar: String = argument.defaultMetavar
+
+  inline given [T](using mirror: RefinedTypeOps.Mirror[T], argument: Argument[mirror.IronType]): Argument[T] =
+    argument.asInstanceOf[Argument[T]]
diff --git a/decline/test/src/io/github/iltotore/iron/DeclineSuite.scala b/decline/test/src/io/github/iltotore/iron/DeclineSuite.scala
new file mode 100644
index 00000000..a1f0450c
--- /dev/null
+++ b/decline/test/src/io/github/iltotore/iron/DeclineSuite.scala
@@ -0,0 +1,23 @@
+package io.github.iltotore.iron
+
+import _root_.com.monovore.decline.Argument
+import _root_.cats.data.Validated.Valid
+import io.github.iltotore.iron.decline.given
+import io.github.iltotore.iron.constraint.numeric.Positive
+import utest.*
+
+object DeclineSuite extends TestSuite:
+  val tests: Tests = Tests {
+
+    test("Argument") {
+      test("ironType") {
+        test("success") - assert(summon[Argument[Int :| Positive]].read("5") == Valid(5)) 
+        test("failure") - assert(summon[Argument[Int :| Positive]].read("-5").isInvalid)
+      }
+
+      test("newType") {
+        test("success") - assert(summon[Argument[Temperature]].read("5") == Valid(5)) 
+        test("failure") - assert(summon[Argument[Temperature]].read("-5").isInvalid)
+      }
+    }
+  }
diff --git a/decline/test/src/io/github/iltotore/iron/RefinedOpsTypes.scala b/decline/test/src/io/github/iltotore/iron/RefinedOpsTypes.scala
new file mode 100644
index 00000000..4b0c33c5
--- /dev/null
+++ b/decline/test/src/io/github/iltotore/iron/RefinedOpsTypes.scala
@@ -0,0 +1,6 @@
+package io.github.iltotore.iron
+
+import io.github.iltotore.iron.constraint.numeric.Positive
+
+opaque type Temperature = Int :| Positive
+object Temperature extends RefinedTypeOps[Int, Positive, Temperature]
\ No newline at end of file
diff --git a/docs/_docs/modules/decline.md b/docs/_docs/modules/decline.md
new file mode 100644
index 00000000..62d3a6ef
--- /dev/null
+++ b/docs/_docs/modules/decline.md
@@ -0,0 +1,72 @@
+---
+title: "Decline Support"
+---
+
+# Skunk Support
+
+This module provides refined types Argument instances for [Decline](https://ben.kirw.in/decline/).
+
+## Dependency
+
+SBT:
+
+```scala 
+libraryDependencies += "io.github.iltotore" %% "iron-decline" % "version"
+```
+
+Mill:
+
+```scala 
+ivy"io.github.iltotore::iron-decline:version"
+```
+
+### Following examples' dependencies
+
+SBT:
+
+```scala 
+libraryDependencies += "com.monovore" %% "decline" % "2.4.1"
+```
+
+Mill:
+
+```scala 
+ivy"com.monovore::decline::2.4.1"
+```
+
+## Argument instances
+
+Iron provides `Argument` instances for refined types:
+
+```scala 
+import cats.implicits.*
+import com.monovore.decline.*
+import io.github.iltotore.iron.*
+import io.github.iltotore.iron.constraint.all.*
+import io.github.iltotore.iron.decline.given
+
+type Person = String :| Not[Blank]
+
+opaque type PositiveInt <: Int = Int :| Positive
+object PositiveInt extends RefinedTypeOps[Int, Positive, PositiveInt]
+
+object HelloWorld extends CommandApp(
+  name = "hello-world",
+  header = "Says hello!",
+  main = {
+    // Defining an option for a constrainted type
+    val userOpt =
+      Opts.option[Person]("target", help = "Person to greet.")
+        .withDefault("world")
+
+    // Defining an option for a refined opaque type
+    val nOpt =
+      Opts.option[PositiveInt]("quiet", help = "Number of times message is printed.")
+        .withDefault(PositiveInt(1))
+
+    (userOpt, nOpt).mapN { (user, n) => 
+      (1 to n).map(_ => println(s"Hello $user!"))
+    }
+  }
+)
+```
diff --git a/docs/sidebar.yml b/docs/sidebar.yml
index 2e7dd4e6..c7b233c1 100644
--- a/docs/sidebar.yml
+++ b/docs/sidebar.yml
@@ -21,6 +21,7 @@ subsection:
       - page: modules/cats.md
       - page: modules/circe.md
       - page: modules/ciris.md
+      - page: modules/decline.md
       - page: modules/jsoniter.md
       - page: modules/skunk.md
       - page: modules/scalacheck.md