Atomic force microscopy allows three-dimensional imaging and measurements of unstained and uncoated biological samples in air or fluid. Using this technology it offers resolution on the nanometer scale and detection of temporal changes in the mechanical properties, i.e. surface stiffness or elasticity in live cells and membranes. Various biological processes including ligand-receptor interactions, reorganization, and restructuring of the cytoskeleton associated with cell motility that are governed by intermolecular forces and their mode of detection will be discussed.