For a physicist noise is not just about sounds. It refers to any random physical process that blurs measurements and, in so doing, stands in the way of scientific knowledge. This short book deals with the most common types of noise, their properties and some of their unexpected virtues. The text assumes that the reader knows the basics of probability theory and explains the most useful mathematical concepts related to noise. Finally, it aims at making this subject more widely known and stimulating interest in its study in young physicists.