Hematopoietic stem cells (HSCs) reside in distinct sites throughout fetal and adult life and give rise to all cells of the hematopoietic system. Because of their multipotency, HSCs are capable of curing a wide variety of blood disorders through hematopoietic stem cell transplantation (HSCT). However, due to HSC heterogeneity, site-specific ontogeny and current limitations in generating and expanding HSCs in vitro, their broad use in clinical practice remains challenging. To assess HSC multipotency, evaluation of their capacity to generate T lymphocytes has been regarded as a valid read-out. Several in vitro models of T cell development have been established which are able to induce T-lineage differentiation from different hematopoietic precursors, although with variable efficiency. Here, we review the potential of human HSCs from various sources to generate T-lineage cells using these different models in order to address the use of both HSCs and T cell precursors in the clinic.