diff --git a/Examples/count-lines/CountLines.swift b/Examples/count-lines/CountLines.swift
index 3289ef221..fae5f845e 100644
--- a/Examples/count-lines/CountLines.swift
+++ b/Examples/count-lines/CountLines.swift
@@ -10,7 +10,11 @@
 //===----------------------------------------------------------------------===//
 
 import ArgumentParser
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 @main
 @available(macOS 12, *)
diff --git a/Plugins/GenerateManual/GenerateManualPluginError.swift b/Plugins/GenerateManual/GenerateManualPluginError.swift
index 43138d2b7..1d6ea2123 100644
--- a/Plugins/GenerateManual/GenerateManualPluginError.swift
+++ b/Plugins/GenerateManual/GenerateManualPluginError.swift
@@ -8,8 +8,11 @@
 // See https://swift.org/LICENSE.txt for license information
 //
 //===----------------------------------------------------------------------===//
-
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 import PackagePlugin
 
 enum GenerateManualPluginError: Error {
diff --git a/Sources/ArgumentParser/Documentation.docc/Articles/GettingStarted.md b/Sources/ArgumentParser/Documentation.docc/Articles/GettingStarted.md
index 136aca619..6f8a0364c 100644
--- a/Sources/ArgumentParser/Documentation.docc/Articles/GettingStarted.md
+++ b/Sources/ArgumentParser/Documentation.docc/Articles/GettingStarted.md
@@ -228,7 +228,11 @@ As promised, here's the complete `count` command, for your experimentation:
 
 ```swift
 import ArgumentParser
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 @main
 struct Count: ParsableCommand {
diff --git a/Sources/ArgumentParser/Documentation.docc/Extensions/AsyncParsableCommand.md b/Sources/ArgumentParser/Documentation.docc/Extensions/AsyncParsableCommand.md
index f6a6238d8..0210ac3c5 100644
--- a/Sources/ArgumentParser/Documentation.docc/Extensions/AsyncParsableCommand.md
+++ b/Sources/ArgumentParser/Documentation.docc/Extensions/AsyncParsableCommand.md
@@ -9,7 +9,11 @@ To use `async`/`await` code in your commands' `run()` method implementations, fo
 The following example declares a `CountLines` command that uses Foundation's asynchronous `FileHandle.AsyncBytes` to read the lines from a file: 
 
 ```swift
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 @main
 struct CountLines: AsyncParsableCommand {
diff --git a/Sources/ArgumentParser/Usage/DumpHelpGenerator.swift b/Sources/ArgumentParser/Usage/DumpHelpGenerator.swift
index e1b562434..271510499 100644
--- a/Sources/ArgumentParser/Usage/DumpHelpGenerator.swift
+++ b/Sources/ArgumentParser/Usage/DumpHelpGenerator.swift
@@ -9,10 +9,15 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if swift(>=5.11)
+#if compiler(>=6.0)
+#if canImport(FoundationEssentials)
+internal import ArgumentParserToolInfo
+internal import class FoundationEssentials.JSONEncoder
+#else
 internal import ArgumentParserToolInfo
 internal import class Foundation.JSONEncoder
-#elseif swift(>=5.10)
+#endif
+#elseif compiler(>=5.10)
 import ArgumentParserToolInfo
 import class Foundation.JSONEncoder
 #else
diff --git a/Sources/ArgumentParser/Usage/MessageInfo.swift b/Sources/ArgumentParser/Usage/MessageInfo.swift
index bb9a4ea1d..da39f1a9c 100644
--- a/Sources/ArgumentParser/Usage/MessageInfo.swift
+++ b/Sources/ArgumentParser/Usage/MessageInfo.swift
@@ -9,15 +9,16 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if swift(>=5.11)
+#if compiler(>=6.0)
+#if canImport(FoundationEssentials)
+internal import protocol FoundationEssentials.LocalizedError
+#else
 internal import protocol Foundation.LocalizedError
-internal import class Foundation.NSError
-#elseif swift(>=5.10)
+#endif
+#elseif compiler(>=5.10)
 import protocol Foundation.LocalizedError
-import class Foundation.NSError
 #else
 @_implementationOnly import protocol Foundation.LocalizedError
-@_implementationOnly import class Foundation.NSError
 #endif
 
 enum MessageInfo {
@@ -119,11 +120,7 @@ enum MessageInfo {
       case let error as LocalizedError where error.errorDescription != nil:
         self = .other(message: error.errorDescription!, exitCode: .failure)
       default:
-        if Swift.type(of: error) is NSError.Type {
-          self = .other(message: error.localizedDescription, exitCode: .failure)
-        } else {
-          self = .other(message: String(describing: error), exitCode: .failure)
-        }
+        self = .other(message: String(describing: error), exitCode: .failure)
       }
     } else if let parserError = parserError {
       let usage: String = {
diff --git a/Sources/ArgumentParser/Usage/UsageGenerator.swift b/Sources/ArgumentParser/Usage/UsageGenerator.swift
index e34b94ee6..c8397505d 100644
--- a/Sources/ArgumentParser/Usage/UsageGenerator.swift
+++ b/Sources/ArgumentParser/Usage/UsageGenerator.swift
@@ -9,9 +9,13 @@
 //
 //===----------------------------------------------------------------------===//
 
-#if swift(>=5.11)
+#if compiler(>=6.0)
+#if canImport(FoundationEssentials)
+internal import protocol FoundationEssentials.LocalizedError
+#else
 internal import protocol Foundation.LocalizedError
-#elseif swift(>=5.10)
+#endif
+#elseif compiler(>=5.10)
 import protocol Foundation.LocalizedError
 #else
 @_implementationOnly import protocol Foundation.LocalizedError
diff --git a/Tests/ArgumentParserUnitTests/DumpHelpGenerationTests.swift b/Tests/ArgumentParserUnitTests/DumpHelpGenerationTests.swift
index fe1ebca6d..c4aeb7985 100644
--- a/Tests/ArgumentParserUnitTests/DumpHelpGenerationTests.swift
+++ b/Tests/ArgumentParserUnitTests/DumpHelpGenerationTests.swift
@@ -83,7 +83,7 @@ extension DumpHelpGenerationTests {
     var opt: Color?
 
     @Option(help: "An optional color with a default value.")
-    var optWithDefault: Color? = .yellow
+    var optWithDefault: Color = .yellow
 
     @Option(help: .init(discussion: "A preamble for the list of values in the discussion section."))
     var extra: Color
diff --git a/Tests/ArgumentParserUnitTests/HelpGenerationTests.swift b/Tests/ArgumentParserUnitTests/HelpGenerationTests.swift
index dc74ddee6..892babe69 100644
--- a/Tests/ArgumentParserUnitTests/HelpGenerationTests.swift
+++ b/Tests/ArgumentParserUnitTests/HelpGenerationTests.swift
@@ -16,7 +16,7 @@ import ArgumentParserTestHelpers
 final class HelpGenerationTests: XCTestCase {
 }
 
-extension Foundation.URL: ArgumentParser.ExpressibleByArgument {
+extension URL: ArgumentParser.ExpressibleByArgument {
   public init?(argument: String) {
     guard let url = URL(string: argument) else {
       return nil
diff --git a/Tools/changelog-authors/ChangelogAuthors.swift b/Tools/changelog-authors/ChangelogAuthors.swift
index 1ab3f6894..54e9dba08 100644
--- a/Tools/changelog-authors/ChangelogAuthors.swift
+++ b/Tools/changelog-authors/ChangelogAuthors.swift
@@ -12,7 +12,11 @@
 #if os(macOS)
 
 import ArgumentParser
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 // MARK: Command
 
diff --git a/Tools/generate-manual/DSL/Document.swift b/Tools/generate-manual/DSL/Document.swift
index 86c43aed0..7b6c66769 100644
--- a/Tools/generate-manual/DSL/Document.swift
+++ b/Tools/generate-manual/DSL/Document.swift
@@ -11,7 +11,11 @@
 
 import ArgumentParser
 import ArgumentParserToolInfo
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 struct Document: MDocComponent {
   var multiPage: Bool
diff --git a/Tools/generate-manual/DSL/Preamble.swift b/Tools/generate-manual/DSL/Preamble.swift
index a75383c0b..96045ab73 100644
--- a/Tools/generate-manual/DSL/Preamble.swift
+++ b/Tools/generate-manual/DSL/Preamble.swift
@@ -11,7 +11,11 @@
 
 import ArgumentParser
 import ArgumentParserToolInfo
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
 struct Preamble: MDocComponent {
   var date: Date
diff --git a/Tools/generate-manual/Extensions/Date+ExpressibleByArgument.swift b/Tools/generate-manual/Extensions/Date+ExpressibleByArgument.swift
index 0d0f5ed08..6f3d96cb5 100644
--- a/Tools/generate-manual/Extensions/Date+ExpressibleByArgument.swift
+++ b/Tools/generate-manual/Extensions/Date+ExpressibleByArgument.swift
@@ -10,9 +10,13 @@
 //===----------------------------------------------------------------------===//
 
 import ArgumentParser
+#if canImport(FoundationEssentials)
+import FoundationEssentials
+#else
 import Foundation
+#endif
 
-extension Foundation.Date: ArgumentParser.ExpressibleByArgument {
+extension Date: ArgumentParser.ExpressibleByArgument {
   // parsed as `yyyy-mm-dd`
   public init?(argument: String) {
     // ensure the input argument is composed of exactly 3 components separated