A theory is described which integrates a wide variety of paradigms that study short-term and long-term serial memory. This theory is based on the ACT-R production system (Anderson, 1993). It assumes that serial lists are represented as hierarchical structures consisting of chunks and items within chunks. Production rules exist to search this structure at any level in a left-to-right manner. In ACT-R memory access depends on a limited-capacity activation process, and errors can occur in the contents of recall because of a partial matching process. These limitations conspire in a number of ways to produce the limitations in immediate memory span: As the span increases, activation must be divided among more elements, activation decays more with longer recall times, and there are more opportunities for positional and acoustic confusions. The theory is shown to be capable of predicting error patterns in serial recall. It also predicts latency patterns in serial recall, retrieval of next item, retrieval of previous item, order judgments, and judgments of list membership. Moreover, it makes unique predictions which are confirmed about interactions between list length and chunk structure.