What order do I play them in??

[Tintin]

Hi, welcome to the forums. I just joined several days ago but I recently asked the same question and have now played through all the games. Play Penumbra: Overture, then Penumbra: Black Plague, and finally Penumbra: Requiem. Requiem is an expansion pack to Black Plague but it's very different (wholly puzzle-based). Enjoy yourself! You're in for a great ride. Between the 3 games you have 20-25 hours of gameplay.