Recently, our understanding of helper/effector T cell differentiation has changed significantly. New subsets of T cells continue to be recognized, including Th17, Treg, and Th9 cells. In addition, the signaling pathways that contribute to their generation continue to be refined. It has become clear that STAT family proteins play a major role in these 'new' T cell fates, along with their critical role in more classical fates. Importantly, genetic studies implicate STATs in autoimmune and primary immunodeficiency diseases in humans. Focusing on how STATs work in concert with other transcription factors will hopefully provide a better mechanistic understanding of the pathogenesis of various autoimmune diseases.