The intrinsic relationship between computer science and brain research fuels a number of philosophically interesting questions. The present essay focuses on two major aspects of this relationship: the enabling role of computer science for brain research on the one hand and the use of computational means to simulate or re-build the brain on the other hand. Even though these two streams of thought are distinct their combination helps to elucidate a deeper problem (or so I hope), namely the question what it is exactly that we can find out by rebuilding the brain.