Immunological memory is manifested by the body's ability to enjoy long-term protection against specific pathogens previously encountered through illness or vaccination. This memory response resides in the long-lived, previously activated memory T and B lymphocytes that are believed to exist in a quiescent state. Recent advances in studies on T cell memory have revealed heterogeneity in the T cells that mediate memory responses that may have implications for the generation and maintenance of these cells over time. This review will present these recent findings on memory T cells in the context of past research and current models for the generation and persistence of memory T cells.