Magnetron sputtering is a mature technique for the deposition of thin films, both at laboratory and industrial level. Conceptually, the technique is quite simple and the process can be summarized in a few lines. A gas discharge is ignited by the application of a high voltage between a cathode and an anode. To increase the ionization efficiency of the electrons emitted from the cathode, a magnetic field is generated by a set of magnets placed behind the cathode. The ions present in the plasma, bombard the cathode which results in the ejection or sputtering of atoms. These sputtered atoms condense on the vacuum chamber walls and on the substrate to form a thin film. Behind this apparent simplicity, a complex interplay between different physical and chemical processes is hidden. This is especially the case when a reactive gas is added to the discharge. This book does not discuss all these processes in detail but provides, through a series of images, an overview of them. The short description accompanying the image can serve as a starting point for a more in-depth study.