The comorbidity of pain and depression has been well established in the literature and is associated with a greater burden to the individual and society than either condition alone. The relationship between pain and depression is quite complex and multiple factors must be considered when trying to disentangle the pain-depression link including shared neurobiology, precipitating environmental factors and cognitive influences. This article aims to provide an overview of the leading neurobiological and psychosocial theories that have advanced our understanding of the link between pain and depression. To this end we describe the shared neurobiological mechanisms in the brain thought to explain the overlap and consider psychological processes and how they inform a cognitive behavioral model. The article also provides an overview of the evidence based treatment for comorbid pain and depression.