The TTT-plot based on failure times from non-repairable units and its theoretical counterpart, the scaled TTT-transform, based on the corresponding life distribution, was presented thirty years ago as a tool for model identification purposes. Since then a number of different applications of TTT-plotting have been presented. Among these are analysis of different aging properties, optimization of age replacement problems and TTT-plotting as a source for creating and studying test statistics. Furthermore, different generalizations have been presented. Among these are applications to repairable units and use of censored failure times. This paper gives an overview of TTT-plotting and a number of practical and theoretical applications with a wide range of references for further reading.