This piece of music is the Etude Op. 10 No. 4 in C# minor by Frederic Chopin. The concept of Etudes or Studies for piano were nothing new, but previously thought of as being exercises for pianists to practice particular techniques. However Chopin took the concept to a whole new level with his Etudes creating pieces which were rewarding to practice and play, and to listen to. All Chopin's Etudes are very difficult to play, but they are fascinating compositions and useful practice for the advanced piano student. In total Chopin wrote 27 Etudes, a set of 12 called Op.10 and another set of 12 called Op.25 and finally a set of 3 etudes - some are a little easier to play than this one, though many are just as difficult. All 27 are available in book form from these links at Sheet Music Plus (US) or The Music Room (UK).