PCSX2-is this for real?

I just found this http://www.pcsx2.net

"PCSX2 is a PlayStation 2 emulator for Windows and Linux. PCSX2 attempts to allow PS2 code to be executed on your computer, thus meaning you can put a PS2 DVD or CD into your computers drive, and boot it up!"

I was wondering what the catch was? Is this for real and is it legal in the US?

Sorry for being full of questions today, but I knew someone on here would know! :D

I do believe that emulators are fully legal if you own the game, however I would double check before doing any downloading!