The behaviour of T cells is not fixed in the germ line, but is highly adaptable depending on experiences encountered during a T cell's life. To understand how different T cell subsets arise and how prior signalling input regulates subsequent T cell behaviour, approaches are required that couple a given T cell state to signals received by the cell, or by one of its ancestors, at earlier times. Here we describe recently developed technologies that have been used to determine the kinship of different T cell subsets and their prior functional characteristics. Furthermore, we discuss the potential value of new technologies that would allow assessment of T cell migration patterns and prior signalling events.