Pain is widespread, multidimensional, and one of the most distressing symptoms patients with cancer face. Pain assessment is the foundation to optimal pain management. Despite evidence-based practice guidelines, inadequate pain assessment is a barrier. Patients should be routinely screened for pain at each encounter. If new, worsening, or persistent pain is present, a comprehensive pain assessment and reassessment should be regularly performed and documented to communicate the pain problem. Patient self-report of pain is the gold standard even in those who are nonverbal or cognitively impaired. Clinicians should follow the Hierarchy of Pain Assessment Framework to guide pain assessment approaches.