Chronic pain is increasingly recognized as an important target for novel therapies. Consequently, it is a growing field of research. Historically, animal models have focused on acute pain, and there is increasing interest in developing and better understanding animal models of chronic pain, including induced and naturally occurring chronic pain. The potential for unexpected chronic pain and its treatment to act as a confounder on research data should be considered. Management of chronic pain in animals remains challenging, due to difficulties in its identification, the availability of effective therapies, and assessment of response to therapy. This chapter provides an overview of our current understanding of chronic pain, including its definition, impact, identification, and treatment.