diff --git a/cmd/asdf/main_test.go b/cmd/asdf/main_test.go
index 321b76350..1a4202240 100644
--- a/cmd/asdf/main_test.go
+++ b/cmd/asdf/main_test.go
@@ -20,7 +20,10 @@ func TestBatsTests(t *testing.T) {
 
 	// Run tests with the asdf binary in the temp directory
 
-	// Uncomment these as they are implemented
+	t.Run("set_command", func(t *testing.T) {
+		runBatsFile(t, dir, "set_command.bats")
+	})
+
 	t.Run("current_command", func(t *testing.T) {
 		runBatsFile(t, dir, "current_command.bats")
 	})
diff --git a/internal/cli/cli.go b/internal/cli/cli.go
index 2ec0d4ca0..7b66dc4f1 100644
--- a/internal/cli/cli.go
+++ b/internal/cli/cli.go
@@ -54,14 +54,35 @@ func Execute(version string) {
 	log.SetFlags(0)
 
 	app := &cli.Command{
+		HideHelp:  true,
 		Name:      "asdf",
 		Version:   version,
 		Copyright: "(c) 2024 Trevor Brown",
 		Authors: []any{
-			mail.Address{Name: "Trevor Brown", Address: "someguy@example.com"},
+			mail.Address{Name: "Trevor Brown"},
 		},
 		Usage:     "The multiple runtime version manager",
 		UsageText: usageText,
+		Action: func(_ context.Context, cmd *cli.Command) error {
+			// If no args, show help
+			if cmd.Args().Len() == 0 {
+				return helpCommand(logger, version, "", "")
+			}
+
+			// Check if first arg matches any command - if so, let urfave/cli handle it
+			firstArg := cmd.Args().Get(0)
+			for _, c := range cmd.Commands {
+				if c.Name == firstArg {
+					return nil
+				}
+			}
+
+			// No matching command - manually invoke CommandNotFound behavior
+			logger.Printf("invalid command provided: %s\n\n", firstArg)
+			helpCommand(logger, version, "", "")
+			cli.OsExiter(1)
+			return cli.Exit("", 1)
+		},
 		Commands: []*cli.Command{
 			{
 				Name: "cmd",
diff --git a/test/set_command.bats b/test/set_command.bats
new file mode 100644
index 000000000..af48eaa82
--- /dev/null
+++ b/test/set_command.bats
@@ -0,0 +1,115 @@
+#!/usr/bin/env bats
+
+load test_helpers
+
+setup() {
+  setup_asdf_dir
+  install_dummy_plugin
+  install_dummy_version "1.0.0"
+  install_dummy_version "1.1.0"
+
+  PROJECT_DIR="$HOME/project"
+  mkdir -p "$PROJECT_DIR"
+
+  cd "$PROJECT_DIR" || exit
+}
+
+teardown() {
+  clean_asdf_dir
+}
+
+@test "set should emit an error when called with incorrect arity" {
+  run asdf set
+  [ "$status" -eq 1 ]
+  [ "$output" = "tool and version must be provided as arguments" ]
+}
+
+@test "set should emit an error when version is not provided" {
+  run asdf set "dummy"
+  [ "$status" -eq 1 ]
+  [ "$output" = "version must be provided as an argument" ]
+}
+
+@test "set should create .tool-versions file in current directory" {
+  run asdf set "dummy" "1.0.0"
+  [ "$status" -eq 0 ]
+  [ -f "$PROJECT_DIR/.tool-versions" ]
+  run cat "$PROJECT_DIR/.tool-versions"
+  [ "$output" = "dummy 1.0.0" ]
+}
+
+@test "set should create .tool-versions file in home directory when --home flag is used" {
+  run asdf set --home "dummy" "1.0.0"
+  [ "$status" -eq 0 ]
+  [ -f "$HOME/.tool-versions" ]
+  run cat "$HOME/.tool-versions"
+  [ "$output" = "dummy 1.0.0" ]
+}
+
+@test "set -u should be an alias for --home" {
+  run asdf set -u "dummy" "1.0.0"
+  [ "$status" -eq 0 ]
+  [ -f "$HOME/.tool-versions" ]
+  run cat "$HOME/.tool-versions"
+  [ "$output" = "dummy 1.0.0" ]
+}
+
+@test "set should update parent directory .tool-versions when --parent flag is used" {
+  echo "dummy 1.0.0" >"$PROJECT_DIR/.tool-versions"
+
+  CHILD_DIR="$PROJECT_DIR/child"
+  mkdir -p "$CHILD_DIR"
+  cd "$CHILD_DIR"
+
+  run asdf set --parent "dummy" "1.1.0"
+  [ "$status" -eq 0 ]
+  [ -f "$PROJECT_DIR/.tool-versions" ]
+  [ ! -f "$CHILD_DIR/.tool-versions" ]
+  run cat "$PROJECT_DIR/.tool-versions"
+  [ "$output" = "dummy 1.1.0" ]
+}
+
+@test "set -p should be an alias for --parent" {
+  echo "dummy 1.0.0" >"$PROJECT_DIR/.tool-versions"
+
+  CHILD_DIR="$PROJECT_DIR/child"
+  mkdir -p "$CHILD_DIR"
+  cd "$CHILD_DIR"
+
+  run asdf set -p "dummy" "1.1.0"
+  [ "$status" -eq 0 ]
+  [ -f "$PROJECT_DIR/.tool-versions" ]
+  [ ! -f "$CHILD_DIR/.tool-versions" ]
+  run cat "$PROJECT_DIR/.tool-versions"
+  [ "$output" = "dummy 1.1.0" ]
+}
+
+@test "set should emit an error when both --home and --parent flags are used" {
+  run asdf set --home --parent "dummy" "1.0.0"
+  [ "$status" -eq 1 ]
+  [ "$output" = "home and parent flags cannot both be specified; must be one location or the other" ]
+}
+
+@test "set should emit an error when --parent is used but no .tool-versions file exists in parent directory" {
+  CHILD_DIR="$PROJECT_DIR/child"
+  mkdir -p "$CHILD_DIR"
+  cd "$CHILD_DIR"
+
+  run asdf set --parent "dummy" "1.0.0"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"No .tool-versions version file found in parent directory"* ]]
+}
+
+@test "set with -h flag should show error for undefined flag" {
+  run asdf set -h "dummy" "1.0.0"
+  [ "$status" -eq 1 ]
+  [[ "$output" == *"flag provided but not defined: -h"* ]]
+}
+
+@test "set should support multiple versions" {
+  run asdf set "dummy" "1.0.0" "1.1.0"
+  [ "$status" -eq 0 ]
+  [ -f "$PROJECT_DIR/.tool-versions" ]
+  run cat "$PROJECT_DIR/.tool-versions"
+  [ "$output" = "dummy 1.0.0 1.1.0" ]
+}