Harbor porpoises (Phocoena phocoena) have a reputation for being inconspicuous and until recently, their behavior has been poorly described, despite their common nearshore occurrence across much of the Northern Hemisphere. For the past seven years we have studied this species reliably in waters near Homer, Alaska, in conjunction with our team in San Francisco (NOAA Fisheries permit #20386). Herein, we describe our sightings and resightings (mark-recapture) to date, and our expanded pilot study defining habitat use and behavior of this species in Kachemak Bay. Additionally, we documented the first seven observations of aerial behavior in this region using still and video imagery. A description of their mating habits in San Francisco Bay revealed that males often become fully or partially airborne as a consequence of their rapid sexual approaches to females (69% of mating attempts, n = 85) and that aerial behavior occurred only in a mating context. Furthermore, males always attempted to copulate by positioning their ventral side on the females’ left side (100% of approaches, n = 142), typically perpendicular to her level position at the surface. Mating may occur while traveling or aggregating for feeding and when calves are present. Researchers should be aware that rapid approaches to a conspecific and aerial behavior may be a sign of mating, rather than foraging, activity. We seek collaborators with photos or videos to identify this high-energy lateralized aerial mating behavior throughout Alaska.