Scanning probe microscopy (SPM) was originally conceived as a method for measuring
atomic-scale surface topography. Over the last two decades, it has blossomed into an
array of techniques that can be used to obtain a rich variety of information about
nanoscale material properties. With the exception of friction measurements, these
techniques have traditionally depended on tip-sample interactions directed normal to
the sample's surface. Recently, researchers have explored several effects arising from
interactions parallel to surfaces, usually by deliberately applying a modulated lateral
displacement. In fact, some parallel motion is ubiquitous to cantilever-based SPM, due to
the tilt of the cantilever. Recent studies, performed in contact, noncontact, and
intermittent-contact modes, provide new insights into properties such as structural
anisotropy, lateral interactions with surface features, nanoscale shear stress and contact
mechanics, and in-plane energy dissipation. The understanding gained from interpreting
this behavior has consequences for all cantilever-based scanning probe microscopies.