This is a graduate textbook on the principles of linear inverse problems, methods of their approximate solution & practical application in imaging. The level of mathematical treatment is kept as low as possible to make the book suitable for a wide range of readers from different backgrounds in science & engineering. Mathematical prerequisites are first courses in analysis, geometry, linear algebra, probability theory & Fourier analysis. The authors concentrate on presenting easily implementable & fast solution algorithms. The book will provide the reader with the appropriate background for a clear understanding of the essence of inverse problems (ill-posedness & its cure) and, consequently, for an intelligent assessment of the rapidly growing literature on these problems.