In this Monograph, Buss and Spencer develop a novel theory of preschool executive function (EF) based on the principles of dynamic systems theory (DST). In this commentary, I discuss how this model contributes to our understanding of EF and highlight challenges that remain to be addressed. First, I discuss Buss and Spencer's model in the context of existing theories, and in terms of the processes thought to underlie developmental improvements in card-sorting. Next, I explore implications for our understanding of the structure of EF in early childhood. Finally, I suggest possible extensions of this approach to later development, including whether and how this work might shed light on relations between individual differences in early EF and later developmental outcomes.