Cancer pain may be classified as nociceptive or neuropathic, although psychological factors play an important role in individual perception. Pain assessment is a systematic clinical evaluation that ends with a diagnosis that emphasizes on the etiology and pathophysiology of the pain complaint. The medical history emphasizes on pain characteristics, cancer history and treatment, and psychological factors such as depression, fear, anxiety, and anger. The clinician should perform a physical examination of the painful sites and of the various systems with special attention to the neurologic and musculoskeletal systems. This systematic approach helps to identify the causes of pain in the cancer patient. A well-illustrated flowchart on metastatic disease has been provided in this chapter.