PROJECT SUMMARY/ABSTRACT The ThymUS 2020 International Conference on Lymphopoiesis, T cell Differentiation and Immune Reconstitution (http://www.thymusmeeting.org/2020) will be held in Wailea Beach, HI from May 2-6, 2020. This is the sixth iteration of the conference, which is the only US-based meeting specifically dedicated to the topic of the thymus and T lymphocyte differentiation, and how these processes are altered during aging and by disease. The conference therefore has a unique scientific content, addressing the highly dynamic and prolific field of adaptive immunity, thymus organogenesis, and T cell development and differentiation, and is relevant for resistance to infection, immune homeostasis from birth to aging, immune reconstitution after therapeutic or pathologic T cell ablation, self-tolerance, and autoimmunity. Importantly, the conference provides several unparalleled features, including (i) a singular focus on thymus biology, which is unique in the Americas; (ii) low cost to all attendees, with additional subsidies provided to trainees; (iii) an extremely rich array of unbiased presentation opportunities, with special attention to trainees; and (iv) a highly stimulating informal interactive environment, providing trainees with access to leaders in the field for the duration of the conference.