Valve will never commit to making a Half-Life movie unless it can base it on an "interesting idea" - but it hasn't ruled the possibility out.
The series' filmic qualities have made the idea of a feature adaptation a fan favourite discussion point - but other than some impressive amateur efforts, nothing official has ever been announced.
However, discussing the idea on Steamcast episode 48, Valve boss Gabe Newell said:
"Certainly it's something we've talked about a bunch. The problem that we have is the same problem we have when we were having this conversations with people outside is we need to have an interesting movie in mind before we commit to it. There's really so little value to making a bad movie about anything.