To review the incidence of cancer pain; assessment of acute, chronic, and breakthrough pain; and provide insight on assessment approaches and reliable and valid instruments for clinical and research settings.Peer-reviewed journal articles, book chapters, Internet.Quality pain management for patients with cancer is dependent on an accurate pain assessment and ongoing reassessment, considering the whole person. Being knowledgeable about evidence-based pain assessment practices is key.Concentrated efforts to address pain assessment barriers and effectively report pain assessments in diverse populations are warranted, especially in this current health care environment when pain assessment is challenging.