This paper proposes that mentalization is usefully understood as a complex, multidimensional capacity that develops and transforms over a lifetime, and that is constantly shaped by relational contexts. The accessibility and maximization of a person's capacity to mentalize is influenced by the dynamic interplay between that person's capacity and the capacities of the other members of that person's relational world. Complexity theory highlights the conditions that facilitate or impede emergent phenomena, like mentalization, and this enhances our understanding of subtle and selective difficulties in an individual's capacity. The value of viewing mentalization through a complexity lens is illustrated clinically.