T cell development in the thymus occurs through a series of events beginning with thymic colonization by migrant precursors and ending with the emigration of functionally competent CD4⁺and CD8⁺T cells to the periphery. It is well accepted that signals through the pre-T cell receptor (pre-TCR) and alpha-beta TCR (αβ TCR) complex play pivotal roles in the maturation of CD4⁻8⁻and CD4⁺8⁺thymocytes, respectively. It is clear that stromal cells constituting the thymic microenvironment provide non-TCR-mediated interactions which are essential for several developmental events. Examples of such will be discussed here in relation to early and late events in T cell development.