Over the past two decades, the subset of scanning probe microscopy termed atomic force microscopy (AFM) has become a ubiquitous tool to image nanoscale structure and to estimate certain mechanical characteristics of biological entities ranging from DNA to tissues. Various modes of imaging and force spectroscopies have been developed to correlate structure, properties, and chemomechanical interactions of molecules and cells in aqueous environments. These advances in AFM have led rapidly to in situ investigations of drug-induced changes in cell structure, membrane stability, and receptor interaction forces.