Similar to all haematopoietic lineages, T cells must be replenished throughout life — a process that is the main function of the thymus. New progenitors are recruited to leave the bloodstream and enter the thymus, then to migrate in a defined pattern within the thymus during differentiation, and finally to return to the blood after maturation. Thereby, directional migration is intrinsically linked to all stages of T-cell differentiation. This review focuses on what is known and what is unknown about the signals that support this migration process in the mouse model of post-natal thymocyte differentiation.