Galaxy-galaxy interactions is one of the leading candidates for triggering nuclear activity in galaxies. Such interactions are thought to be able to bring a fresh supply of gas to the center of a galaxy to fuel its resident supermassive black hole. Optical observations, however, do not reveal direct evidence for interactions among the majority of active galaxies. On the other hand, neutral atomic hydrogen (HI) gas has proven to be an exquisite tracer of galaxy-galaxy interactions, even when no such interactions are visible in the optical. Here, we describe our systematic HI imaging surveys of galaxies hosting active galactic nuclei (AGNs) and quasi-stellar objects (QSOs), and present a few illustrative results.