Yes, you can play Half-Life 2 offline. But you would initially require an Internet connection to download and install the game via Steam since Half-Life 2 is powered by this platform. Steam is required to authenticate your game when you play it for the first time. After you have installed and authenticated Half-Life 2 via Steam, you can switch to Offline Mode to play without an Internet connection. Please follow these steps: 1. Launch the Steam client software and log into your Steam account. 2. Click the gear icon in the upper right-hand corner to go to Steam settings. 3. Click on the interface named “Go Offline…” 4. Steam will prompt you to restart in offline mode. Now, you can launch Half-Life 2 offline, and you do not require an Internet connection to play the campaign unless there are future updates that require you to go online for installation. Remember, however, that while playing offline, features that require a connection like achievements or multiplayer modes won't be available. This is also true if Steam needs to update Half-Life 2 – you'll need to go online for the update to be installed. If you have any mods for Half-Life 2 that require an Internet connection, you may not be able to use them in Offline Mode. So, while you will need internet to set things up initially and handle updates, you can definitely play Half-Life 2 offline when needed.