A precise measurement of the immunological receptor diversity present in a sample is obtained by sequence analysis. Samples of interest are generally complex, comprising more than 102, 103, 104, 105, 106, 107, 108, 109, 1010, 1011, 1012 or more different sequences for a receptor of interest. Immunological receptors of interest include immunoglobulins, T cell antigen receptors, and major histocompatibility receptors. The specific composition of immunological receptor sequence variations in the sample can be recorded and output. The composition is useful for predictive, diagnostic and therapeutic methods relating to the immune capabilities and history of an individual. Such predictions and diagnoses are used to guide clinical decisions.