T he ability to tailor the chemical composition and structure of a surface at the nanometer length scale is essential for fabricating novel nanomaterials, understanding underlying nano-science and engineering, and developing integrated systems for demanding applications. Dip-pen nanolithography (DPN), based upon an atomic force microscope, has recently evolved as a unique tool that allows one to routinely pattern an extraordinary array of materials onto all manner of surfaces at the sub-100-nm to many-micrometer length scale. This chapter briefly reviews the rapid growth of the research field of DPN with particular emphasis on biological applications.