Visual observations of nocturnal species such as owls can be difficult. Knowledge of vocalizations associated with particular behaviours is therefore an extremely useful tool in studying owls in the field. For this purpose, I studied the vocalizations and behaviours of the Great Horned Owl Bubo virginianus, collecting observations on a female human-imprinted individual and wild pairs. Spectrographically, Great Horned Owl calls were divided into three main categories: hoots, chitters, and squawks. These categories were further subdivided into five types of hoots, four types of chitters, and five types of squawks based on inflection, number of syllables, duration, pitch, volume, and behavioural context. Two types of non-vocal communication were also distinguished: hisses and bill clacking. Although owl vocalizations are generally considered innate and variation between individuals should not differ in basic makeup and behavioural context, further verification on wild owls is encouraged.