This document discusses pain assessment. It begins by outlining six objectives related to explaining pain pathophysiology, differentiating between acute and chronic pain, discussing physiologic pain responses, assessing pain as a vital sign, interviewing patients about their pain experience, and performing a physical assessment. It then defines pain and discusses physiologic pain responses and classifications including acute, chronic, cancer, nociceptive, neuropathic, and intractable pain. It also covers the seven dimensions of pain and psychosocial factors affecting pain perception. Finally, it discusses various pain assessment tools.