William James was a generative figure for both psychology and philosophy. His vision of mind as personal, embodied, relational, enacted, and continuously in flux challenged earlier empiricism’s account of elementary sensation and influenced later developments in philosophy (e.g., phenomenology) and psychology (e.g., Gestalt and ecological psychology). In his major works, James treated consciousness as a flow, the self as a dynamic plurality, and ideas as instruments of action in the midst of things. His radical empiricism insisted that relations are as real as substantive elements, opening a space for altered states of consciousness, mystical experience, and the complexities of the mind more generally. Over a century after his death, James’s work remains a powerful stimulant to broaden psychological inquiry and attend to experience in all its depth.