Anaphora resolution is the process of determining the referent of anaphors, such as definite noun phrases and pronouns, in a discourse. Computational linguists, in modeling the process of anaphora resolution. have proposed the notion of focusing. Focusing is the process, engaged in by a reader of selecting a subset of the discourse items and making them highly available for further computations. This paper provides a cognitive basis for anaphora resolution and focusing. Human memory is divided into a short-term, an operating, and a long-term memory. Short-term memory can only contain a small number of meaning units and its retrieval time is fast. Short-term memory is divided into a cache and a buffer. The cache contains a subset of meaning units expressed in the previous sentences and the buffer holds a representation of the incoming sentence. Focusing is realized in the cache that contains a subset of the most topical units and a subset of the most recent units in the text. The information stored in the cache is used to integrate the incoming sentence with the preceding discourse. Pronouns should be used to refer to units in focus. Operating memory contains a very large number of units but its retrieval time is slow. It contains the previous text units that are not in the cache. It comprises the text units not in focus. Definite noun phrases should be used to refer to units not in focus. Two empirical studies are described that demonstrate the cognitive basis for focusing, the use of definite noun pphrases to refer to antecedents not in focus. and the use of pronouns to refer to antecedents in focus.