In computer programming, an iterator is an object that enables a programmer to traverse a container, particularly lists. Various types of iterators are often provided via a container's interface. Though the interface and semantics of a given iterator are fixed, iterators are often implemented in terms of the structures underlying a container implementation and are often tightly coupled to the container to enable the operational semantics of the iterator. An iterator performs traversal and also gives access to data elements in a container, but does not itself perform iteration (i.e., not without some significant liberty taken with that concept or with trivial use of the terminology).

An iterator is behaviorally similar to a database cursor. Iterators date to the CLU programming language in 1974.