Nearly 30 years ago, single molecules were first detected optically, but how do we really detect a single molecule today, and what good is it? It is an amazing fact that you can even detect single molecules with your own eyes. When a new regime of science is breached, surprises often occur: single molecules show amazing dynamics, blink on and off, and can be controlled by light. Far from being only an esoteric effect, these “switching properties” of molecules can be used to obtain “super-resolution” and thus to circumvent the fundamental optical diffraction limit, roughly half the wavelength used. Essentially, with tiny single-molecule light sources decorating a structure, the on/off process is used to light up only subsets at a time, and a pointillist reconstruction reveals the hidden nanometer-scale structure, opening up a new frontier.