Following activation, CD4+ T cells differentiate into different lineages of helper T (T(H)) cells that are characterized by distinct developmental regulation and biological functions. T(H)17 cells have recently been identified as a new lineage of effector T(H) cells, and they have been shown to be important in immune responses to infectious agents, as well as in various immune diseases. Over the past two to three years, there has been a rapid progress in our understanding of the differentiation programme of T(H)17 cells. Here, I summarize our current knowledge of the unique gene expression, cytokine-mediated regulation and transcriptional programming of T(H)17 cells, and provide my personal perspectives on the future studies that are required to elucidate this lineage in more detail.