DNA is more than a blueprint for living organisms. In the right hands, it can be used as a self-assembling, nanoscale building material with exquisite design properties. Over the past 15 years, DNA nanotechnology has emerged as one of the most promising platforms for the rational design of nanoscale devices. By “programming” DNA sequences to take advantage of DNA’s inherent complementarity (“A’s bind to T’s; C’s bind to G’s”), DNA can be made to precisely fold into complex shapes with rich functionality, giving nanoengineers precise control over many aspects of a design, such as size, shape, surface charge, surface hydrophobicity, choice of functional elements, and their spatial arrangement. Because a wide variety of molecular species can now be attached to DNA via a growing number of oligonucleotide chemistries, it can be used as a self-organizing substrate that enables a wide array of molecular species to be integrated into sophisticated macromolecular devices.