This entry provides a concise presentation and discussion of the concept of determinism. The starting point is a general overview of the notion, aiming to distinguish various senses of determinism and to pin down their key components. In particular, determinism and indeterminism in physics are considered. Physical determinism is then contrasted with determinism as a thesis formulated at the metaphysical level. In the second part an illustration is offered of the relevance of determinism (or its failure) in the context of the philosophical and scientific study of the nature of human individuals. The debate concerning free will is used, in particular, as an example of the role that determinism and indeterminism play in the context of specific views of the connection between people’s reasons and their choices and actions.