During the last few years the Atomic Force Microscope (AFM) has become capable of routinely obtaining atomic resolution when operated with a vibrating cantilever (ac-mode). Local measurement of the tip-sample force (force spectroscopy) is a powerful tool for investigations of contact phenomena at the atomic scale that are important in fields like friction, tribology, atom manipulation and chemical bond formation. This paper reviews several aspects of the AFM technique such as tip-surface forces, force sensors, operation modes and contrast effects. A study of the Si(111)7 x 7 reconstruction is presented as an example of high resolution AFM imaging.