Sleep disturbance is one of the most common comorbid problems for chronic pain patients. The association between the two phenomena has long been recognized, but the nature of the relationship is not well-understood. Many agree that the relationship is likely bidirectional. In this review, we focus on one side of the relationship: whether and how disordered sleep adversely impacts pain. We discuss the available evidence from the epidemiologic, clinical, and human, as well as infrahuman laboratory studies. Generally, the literature supports the positive relationship between poor sleep and increased pain. Sleep deprivation also seems to attenuate analgesic effects of medications. Research delineating the causal or associative relationship between sleep and pain is still preliminary at this time. Continuing efforts in both experimental and clinical research are needed to develop a translationally meaningful understanding of how poor sleep impacts pain.