Over the last 20 years, a large amount of research has been conducted in an attempt to uncover the cognitive abilities of the domestic dog. While substantial advancements have been made, progress has been impeded by the fact that little is known about how dogs visually perceive their external environment. It is imperative that future research determines more precisely canine visual processing capabilities, particularly considering the increasing number of studies assessing cognition via paradigms requiring vision. This review discusses current research on visual cognition and emphasizes the importance of understanding dog visual processing. We review several areas of vision research in domestic dogs, such as sensitivity to light, visual perspective, visual acuity, form perception, and color vision, with a focus on how these abilities may affect performance in cognition tasks. Additionally, we consider the immense diversity seen in dog morphology and explore ways in which these physical differences, particularly in facial morphology, may result in, or perhaps even be caused by, different visual processing capacities in dogs. Finally, we suggest future directions for research in dog vision and cognition.