Humpback whales produce two different types of vocalizations with apparent difference functions: songs and social sounds. There is also the potential to use the sounds of their environment, such as surf noise during migration along coasts, though this has not been demonstrated. The Humpback Whale Acoustic Research Collaboration (HARC) is a series of well-controlled, multiplatform experiments designed to improve our understanding of how humpback whales use sound, both vocalizations and sounds of their environment. There have been two major experiments with humpback whales migrating along the east coast of Australia. Whales passing within 10 km were tracked acoustically and visually during daylight hours in conjunction with behavioral observations, and DTAGs were used on some whales to record their 3D movements and the sound field to which they were exposed. There was also playback of social sounds and full characterization of the acoustics of the environment, including the ambient noise exposure. Preliminary results of interactions between singing and nonsinging whales, the use of song as a spacing mechanism, responses to playback, and context of social sounds will be discussed. [Research supported by ONR and DSTO.]