The ability to tailor the chemical composition and structure of a surface on the 1-100 nm length scale is important to researchers studying topics ranging from electronic conduction, to catalysis, to biological recognition in nanoscale systems. Dip-pen nanolithography (DPN) is a new scanning-probe based direct-write tool for generating such surface-patterned chemical functionality on the sub-100 nm length-scale, and it is a technique that is accessible to any researcher who can use an atomic force microscope. This article introduces DPN and reviews the rapid growth of the field of DPN-related research over the past few years. Topics covered range from the development of new classes of DPN-compatible chemistry, to experimental and theoretical advances in the understanding of the processes controlling tip-substrate ink transport, to the implementation of micro-electro-mechanical system (MEMS) based strategies for parallel DPN applications.