We examine the biological nature, evolution, and increasing complexity of agency, tracing its historical development and theoretical implications. The chapter explores how agency emerged as both a product of an organism’s constitutive organization and a force driving its evolutionary continuity. The discussion addresses the defining characteristics of agency, highlighting its role in biological interactions, ecological networks, and the transition from simple to complex forms of life. Special attention is given to the relationship between motility, sensory systems, and constitutive development, emphasizing the evolutionary pressures that shaped complexification of agency in animals. Finally, we outline future research directions, particularly in synthetic biology and interdisciplinary collaborations, to further investigate agency’s origins and transformations. By integrating insights from biology, philosophy, and artificial intelligence, this work aims to refine the conceptual framework of agency and inspire new empirical studies on its role in evolution.