Optical microscopy remains one of the most powerful research tools in the biological and material sciences. The main advantage of optical techniques is that they enable noninvasive studies on micrometer length scales under native environmental conditions. Their major drawback is that the diffraction of light limits the spatial resolution to about 100 nanometers, preventing visualization of smaller species such as single molecules and molecular assemblies. For many years, scientists searched for a complementary technique with the high resolution of electron microscopy that would operate in a physiologically relevant environment. With the development of scanning probe or proximal probe techniques, and in particular atomic force microscopy (AFM) in 1986, a new era of microscopy began.