Over ten years ago, Daniel Loss and David DiVincenzo proposed using the spin of a single electron as a quantum bit. At the time of the proposal, it was not possible to trap a single electron in a device and measure its spin, let alone demonstrate control of quantum coherence. In this talk I will describe recent progress in the field, focusing on a new method for single spin control that has been developed by my group at Princeton. The method is based on quantum interference and implements spin-interferometry on a chip. We use an avoided crossing as a quantum mechnical beam splitter, resulting in spin rotations that are orders of magnitude faster than conventional electron spin resonance.