diff --git a/src/Application.php b/src/Application.php
index 99931b2..c2bb186 100644
--- a/src/Application.php
+++ b/src/Application.php
@@ -174,6 +174,37 @@ public function add(Command $command, string $alias = '', bool $default = false)
         return $this;
     }
 
+    /**
+     * Set the default command.
+     *
+     * @param string $commandName The name of the default command
+     *
+     * @return self The application
+     *
+     * @throws InvalidArgumentException If the specified command name does not exist
+     */
+    public function defaultCommand(string $commandName): self
+    {
+        if (!isset($this->commands[$commandName])) {
+            throw new InvalidArgumentException(sprintf('Command "%s" does not exist', $commandName));
+        }
+
+        $this->default = $commandName;
+
+        return $this;
+    }
+
+    /**
+     * Get the default command.
+     *
+     * @return string|null The name of the default command, or null if not set
+     */
+    public function getDefaultCommand(): ?string
+    {
+        return $this->default;
+    }
+
+
     /**
      * Groups commands set within the callable.
      *
diff --git a/tests/ApplicationTest.php b/tests/ApplicationTest.php
index 22bb2f9..0db09ff 100644
--- a/tests/ApplicationTest.php
+++ b/tests/ApplicationTest.php
@@ -305,4 +305,21 @@ protected function newApp(string $name, string $version = '')
 
         return $app->io(new Interactor(static::$in, static::$ou));
     }
+
+    public function testDefaultCommand()
+    {
+        $app = $this->newApp("test");
+
+        // Add some sample commands to the application
+        $app->command('command1');
+        $app->command('command2');
+
+        // Test setting a valid default command
+        $app->defaultCommand('command1');
+        $this->assertEquals('command1', $app->getDefaultCommand());
+
+        // Test setting an invalid default command
+        $this->expectException(InvalidArgumentException::class);
+        $app->defaultCommand('invalid_command');
+    }
 }