T cells are a crucial part of the adaptive immune system and their potential to eradicate pathogens and malignant cells is now extensively exploited as an immunotherapeutic tool. T cells are derived from hematopoietic (blood-forming) stem cells and perturbations during their development can result in immunodeficiencies or T cell leukemias. The overall aim of this project is to uncover the molecular mechanisms that induce and control human T cell development in both normal and malignant settings. By obtaining insights into key mechanisms that drive human T cell development, we not only wish to gather new fundamental knowledge but also aim to utilize these findings towards the design of novel therapeutic applications.