Interleukin 2 and its receptor play a crucial role in the growth and differentiation of many cells such as lymphocytes T and B, NK cells, macrophages and monocytes. Il-2 receptor (Il-2R) is involved in Il-2 induced cellular signalling. We discuss the Il-2R structure, function of three distinct subunits and the complex pathways that link the cell surface receptor to the nuclear proto-oncogene production.