Atomic force microscopy (AFM) is a scanning probe microscopy developed in the 80s by Gerd Binnig, Calvin Quate and Christoph Gerber. It is certainly the most versatile scanning probe microscopy because it can be employed in many environments, from vacuum (to investigate surfaces with atomic resolution), to aqueous solution (for experiments in biology). This book is addressed at students or researchers who want to deepen their understanding of the peculiar physical aspects of the various measurement modes in AFM that are often not discussed extensively in topical text books. Models for contact and adhesion between bodies are described in detail, so as done for the contact mode, the lateral force mode and the kinetic modes: a large section is dedicated to the physics of the harmonic oscillator interacting with a surface. A brief discussion about the technical aspects is also presented, without going into detail, as these are widely available elsewhere, in textbooks and even on internet sites.