Pain in children is underestimated and undertreated because of lack of pain assessment tools. Pain assessment depends on the cognitive development of the child being tested, clinical context, and pain typology. For children older than age 6 years, pain assessment is based on a self-report. For children younger than age 6 years, behavioral pain scales are needed to assess pain. Numerous pain scales exist. Many are reliable and some are recommended, but all have specific conditions for their use. In this article, we review the available pain scales for children from birth to adolescence. We provide the validity criteria of each pain scale to help caregivers use the adapted tools. We then propose a synthesis of the reliable tools to use based on the pain context. [Pediatr Ann. 2017;46(10):e387-e395.].