The immune system protects our bodies against infectionsand cancers. This review introduce readers to the thymus

– a primary lymphoid organ – which is the site of developmentand maturation of functional T lymphocytes. Progenitorstem cells arise from the bone marrow and undergo sequentialdevelopment in the thymus where non-self-reactiveT cells are selected. Subsequently, post selection and maturation,the mature T cells exit the thymus as na¨ıve T cells intothe peripheral lymph nodes. Studies on the thymus are likelyto enhance our understanding of T cell development and reducedisease burdens by improving the cellular immune response.