Flexibility is a defining characteristic of our species. The current literature presents cognitive flexibility as having several meanings; this lack of a single definition may hinder work on understanding the concept. In this article, I begin with describing the variability–stability–flexibility pattern in the development of various abilities and then argue that as part of this chain, flexibility can be considered a property of the cognitive system and not in itself an ability. The implications of and challenges to this view are discussed. This view can foster progress in the understanding of cognitive flexibility: It can serve as a unifying framework in which to study the dynamic flow of stability and flexibility in the functioning of the cognitive system.