Immune-based strategies for treating and preventing cancer are increasingly being tested and include cancer vaccination, adoptive T cell therapy, and cytokine therapy. An important component of testing and development of immune-based strategies is monitoring the immunologic response. The ability to monitor T cell immunity has been suboptimal. The measurement of tumor-specific immunity will aid in defining which strategies should be moved forward in clinical trials and which should be eliminated or evaluated further in the preclinical realm. Immunologic monitoring is necessary for determining if an approach has immunologic efficacy and ultimately whether immunologic responses correlate with a clinical response. This article discusses several important elements of measuring T cell immunity such as validation principles, laboratory issues, current approaches, and new paradigms and concepts for future testing. Informative immunologic monitoring of T cells will be one of the driving forces in advancing the field of tumor immunology.