Atomic force microscopy (AFM) allows the surfaces of individual proteins to be imaged in aqueous solution with a lateral resolution < 0.5 nm and a vertical resolution < 0.1 nm which is sufficient to directly observe both, tertiary structural arrangement and secondary structural elements of native proteins. Conformational changes of individual proteins were observed by time-lapse AFM and multivariate statistical classification unraveled major conformations of their variable structural elements. We further report on the possibility to image protein complexes before and after the removal
of individual subunits using the AFM tip as a nanotool. Based on these results, single molecule imaging and single molecule forcespectroscopy capabilities of the AFM have been combined providing novel insights into the inter- and intramolecular interactions of proteins. Applied to membrane proteins, this technique allows to measure forces required to unfold secondary structural elements and to record unfolding pathways of individual proteins.