Determinism is a philosophical view, where all events are determined completely by previously existing causes. Deterministic theories throughout the history of philosophy have developed from diverse and sometimes overlapping motives and considerations. The opposite of determinism is some kind of indeterminism and even more so nondeterminism (aka randomness). Determinism shares similarities with eternalism with a focus on particular events rather than the future as a concept entirely. Determinism is often contrasted with free will, although some philosophers claim that the two are compatible.

Determinism is often used to mean causal determinism, which in physics is known as cause-and-effect. This is the concept that events within a given paradigm are bound by causality in such a way that any state of an object or event is completely determined by its prior states. This meaning can be distinguished from other varieties of determinism mentioned below.

Debates about determinism often concern the scope of determined systems; some maintain that the entire universe is a single determinate system, and others identifying more limited determinate systems (or multiverse). Historical debates involve many philosophical positions and varieties of determinism. They include debates concerning determinism and free will, technically denoted as compatibilistic (allowing the two to coexist) and incompatibilistic (denying their coexistence is a possibility).

Determinism should not be confused with the self-determination of human actions by reasons, motives, and desires. Determinism is about interactions which affect our cognitive processes in our life. It is about the cause and the result of what we have done. Cause and result are always bound together in cognitive processes. It assumes that if an observer has sufficient information about an object or human being, that such an observer might be able to predict every consequent move of that object or human being. Determinism rarely requires that perfect prediction be practically possible.