Atomic force microscopy is being increasingly used to explore the physical properties of biological structures. This technique involves the application of a force to the sample and a monitoring of the ensuing deformation process. The available experimental setups can be broadly divided into two categories, one of which involves a stretching and the other an indentation of the organic materials. In this review, we will focus on the indentation technique and will illustrate its application to biological materials with examples that range from single molecules to living cells.