The past decade has seen an explosion in the use of single-molecule approaches to study complex biological processes. One such approach—optical trapping—is particularly well suited for investigating molecular motors, a diverse group of macromolecular complexes that convert chemical energy into mechanical work, thus playing key roles in virtually every aspect of cellular life. Here we describe how to use high-resolution optical tweezers to investigate the mechanism of the bacteriophage φ29 DNA packaging motor, a ringshaped ATPase responsible for genome packing during viral assembly. This system illustrates how to use single-molecule techniques to uncover novel, often unexpected, principles of motor operation.