diff --git a/AGENTS.md b/AGENTS.md
index 43955ed..5b84e98 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -218,3 +218,26 @@ When behavior changes:
 If a product decision would materially affect persistence compatibility,
 GitHub writes, AI data exposure, destructive behavior, or default keybindings,
 ask the repository owner rather than guessing.
+
+## Semantic versioning
+
+The application version lives in `version.go` and must use Semantic Versioning
+in `MAJOR.MINOR.PATCH` form.
+
+- Keep the major version at `0` until the repository owner explicitly requests
+  a `1.0.0` or later release.
+- Increment `MINOR` and reset `PATCH` to zero for a completed new
+  backward-compatible feature. During `0.x`, also use a minor increment for an
+  intentional breaking change and document that break.
+- Increment `PATCH` for a completed backward-compatible bug fix, refinement,
+  or other non-feature change.
+- Apply one version increment per complete logical change, not per user prompt.
+  Follow-up questions and refinements that finish the same feature share that
+  feature's single version increment.
+- Before incrementing, determine the logical change boundary from the
+  conversation and current work. When the boundary is unclear and Jujutsu is
+  available, inspect the current change and its parent read-only; an empty
+  described parent may identify the feature being developed. Never mutate
+  Jujutsu history merely to determine a version.
+- If the current logical change already contains the appropriate version
+  increment, do not increment it again for another prompt in that same change.
diff --git a/README.md b/README.md
index 424d79d..b56e762 100644
--- a/README.md
+++ b/README.md
@@ -134,6 +134,7 @@ Adjust polling or inspect all command-line options:
 
 ```sh
 diple --poll 15s
+diple --version
 diple --help
 ```
 
diff --git a/cli.go b/cli.go
index 640570e..a362ef9 100644
--- a/cli.go
+++ b/cli.go
@@ -8,6 +8,17 @@ import (
 
 var completionShells = []string{"bash", "zsh", "fish"}
 
+func handleVersionCommand(args []string, output io.Writer) (bool, error) {
+	if len(args) == 0 || args[0] != "--version" {
+		return false, nil
+	}
+	if len(args) != 1 {
+		return true, fmt.Errorf("usage: diple --version")
+	}
+	_, err := fmt.Fprintf(output, "diple %s\n", dipleVersion)
+	return true, err
+}
+
 func handleCompletionCommand(args []string, output io.Writer) (bool, error) {
 	if len(args) == 0 || args[0] != "completion" {
 		return false, nil
@@ -55,6 +66,7 @@ func writeCLIHelp(output io.Writer, defaults Config, configPath string) {
 
 Usage:
   diple [options]
+  diple --version
   diple completion <bash|zsh|fish>
   diple help
 
@@ -92,6 +104,7 @@ Local state:
 
 Other:
   -h, --help                Show this help and exit.
+  --version                 Show the application version and exit.
 
 Boolean options accept explicit values, for example --cache=false.
 Command-line options override TOML settings. GH_REPO is used only when
@@ -158,7 +171,7 @@ _diple_completion() {
             ;;
     esac
 
-    local options="--repo --all --limit --poll --endpoint --theme --dashboard-mode --thread-list-width --fold-resolved --compact-reviews --path-scroll --path-scroll-interval --editor-mode --config --cache --cache-max-age --cache-dir --help -h"
+    local options="--repo --all --limit --poll --endpoint --theme --dashboard-mode --thread-list-width --fold-resolved --compact-reviews --path-scroll --path-scroll-interval --editor-mode --config --cache --cache-max-age --cache-dir --version --help -h"
     COMPREPLY=($(compgen -W "${options}" -- "${current}"))
 }
 complete -F _diple_completion diple
@@ -202,6 +215,7 @@ _diple() {
     '--cache=[enable local read cache]:boolean:(true false)' \
     '--cache-max-age[maximum offline cache age]:duration:' \
     '--cache-dir[local read-cache directory]:directory:_directories' \
+    '--version[show application version]' \
     '(-h --help)'{-h,--help}'[show help]'
 }
 
@@ -234,5 +248,6 @@ complete -c diple -l config -r -F -d 'TOML configuration file'
 complete -c diple -l cache -d 'Enable local read cache'
 complete -c diple -l cache-max-age -x -d 'Maximum offline cache age'
 complete -c diple -l cache-dir -r -a '(__fish_complete_directories)' -d 'Local read-cache directory'
+complete -c diple -l version -d 'Show application version'
 complete -c diple -s h -l help -d 'Show help'
 `
diff --git a/cli_test.go b/cli_test.go
index cee0dd5..0f954fa 100644
--- a/cli_test.go
+++ b/cli_test.go
@@ -2,10 +2,34 @@ package main
 
 import (
 	"bytes"
+	"regexp"
 	"strings"
 	"testing"
 )
 
+func TestVersionCommandPrintsSemanticVersion(t *testing.T) {
+	var output bytes.Buffer
+	handled, err := handleVersionCommand([]string{"--version"}, &output)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !handled || output.String() != "diple "+dipleVersion+"\n" {
+		t.Fatalf("version output = %q, handled=%t", output.String(), handled)
+	}
+	if !regexp.MustCompile(`^0\.(0|[1-9][0-9]*)\.(0|[1-9][0-9]*)$`).MatchString(dipleVersion) {
+		t.Fatalf("version %q is not a pre-1.0 semantic version", dipleVersion)
+	}
+}
+
+func TestVersionCommandRejectsAdditionalArguments(t *testing.T) {
+	handled, err := handleVersionCommand(
+		[]string{"--version", "--help"}, &bytes.Buffer{},
+	)
+	if !handled || err == nil || !strings.Contains(err.Error(), "usage: diple --version") {
+		t.Fatalf("handled=%t error=%v", handled, err)
+	}
+}
+
 func TestCompletionCommandGeneratesSupportedShells(t *testing.T) {
 	for _, shell := range completionShells {
 		t.Run(shell, func(t *testing.T) {
@@ -65,6 +89,7 @@ func TestCLIHelpIsGroupedAndActionable(t *testing.T) {
 		"Appearance and navigation:",
 		"Local state:",
 		"diple completion <bash|zsh|fish>",
+		"--version",
 		"--repo OWNER/REPOSITORY",
 		"--cache=false",
 		"gh auth login",
diff --git a/main.go b/main.go
index 9cf46c3..fea7e86 100644
--- a/main.go
+++ b/main.go
@@ -11,6 +11,12 @@ import (
 )
 
 func main() {
+	if handled, err := handleVersionCommand(os.Args[1:], os.Stdout); handled {
+		if err != nil {
+			exitf("%v", err)
+		}
+		return
+	}
 	if handled, err := handleCompletionCommand(os.Args[1:], os.Stdout); handled {
 		if err != nil {
 			exitf("%v", err)
diff --git a/version.go b/version.go
new file mode 100644
index 0000000..4a7e09e
--- /dev/null
+++ b/version.go
@@ -0,0 +1,3 @@
+package main
+
+const dipleVersion = "0.1.0"