To play HL2..

[shade.alchemist]

To play HL2, do you need a permanent internet connection?

I've heard that you need to have a Internet connection to register the game on steam, but after the registration, do you still need the internet connection to play??

I hope you only need the internet to register the game... Needing the internet for an offline game would suck

 

[hynsey]

You only need the net connection to register your game through steam. Once registered you can play in offline mode, although if you want to receive any updates you would have to run Steam in online mode for a time to get them.