From Johann Sebastian Bach's Well Tempered Clavier, also known as the 48 Preludes and Fugues, this is the 2nd Fugue from Book 1. It is therefore in the key of C minor (since they go major and then minor in every key starting from C, and it has 3 "voices" or parts. On mfiles you can find the corresponding Prelude No.2 in C minor from Book 1 for this Fugue, and together the pair are catalogued as BWV 847.
Although there are some easier preludes and fugues in the set, much of Bach's Well-Tempered Clavier is quite challenging to play. However the complete set has for a long time been considered a must for any serious student of piano. Some other preludes and fugues from the set are available on mfiles if you check the Bach page or Classical Sheet Music page. If you have aspirations to be a good classical pianist then we recommend getting the complete Well-Tempered Clavier which comes in two books. Here are links on "sheet music plus" to Book 1 and Book 2 of the Well-Tempered Clavier.
Here is a video of Bach's Fugue No.2 from book 1 as a piano roll animation:
The audio controls below allow you to play the mp3 version of Bach's Fugue No.2 in C minor from Book 1 or you can download the MP3 file. You can also download the midi version of Bach's Fugue No.2 in C minor from Book 1 or alternatively edit/play the midi file.
The image below is the first page of the sheet music, and here you can download the full sheet music for Bach's Fugue No.2 from book 1 in PDF format.