Because pre-academic and social-emotional capabilities at kindergarten entry predict later academic and social success, there has been great concern with the level of "readiness" at kindergarten entry. Many states require a kindergarten readiness assessment (KRA). However, how readiness is defined, who or what entity is doing the defining, and how this information is used varies greatly. Differences in prevailing theories about how young children learn have led to variations in definitions over time, as well. This brief explores the existing definitions of readiness and the uses of readiness assessment data. The strengths and limitations of each of these approaches is closely examined. Suggestions for defining and measuring readiness and using KRAs follow.