This chapter describes behavioral assessment and approaches to management of acute pain, chronic pain, and sickness behaviors. Acute pain behaviors in cats can be evaluated using a range of behavioural and physiological variables. Chronic primary pain is multifactorial: biological psychological and social factors contribute to the pain syndrome. Scales for both general health-related quality of life and specific conditions have been developed and partially validated for cats. Common sickness behaviors across species include fever, anorexia, inactivity, and decreased social contact. Moreover, studies have shown that many cats with chronic visceral pain can be effectively managed without any diet change. Effective multimodal environmental modification creates conditions that permit the patient to feel safe, and to have unrestricted access to species-appropriate novelty, activity, and interactions with other animals. Vulnerability for a chronic pain condition can develop after significant adverse experiences, particularly early in life.