Linux/Windows Games On Steam

Quick question that I haven't been able to find a straight-forward answer to. If I buy a game on Steam that has Windows AND Linux support, can I play it on both operating systems or do I have to buy it for each?

You can play it on both if it has the "steamplay" tag.

yep, both, just need to download and install, steam gives you the right to play on both systems with one purchase