On Invariants of Quark and Lepton Mass Matrices in the Standard Model

In this article I present the motivation for introducing the invariant functions of mass matrices, based on my own work, and give some examples. Since their introduction in 1985, in the framework of the standard electroweak model, they have been used by many authors. Some authors have gone further along this path and have studied the extensions of this concept to frameworks beyond the standard model. I hope, in the near future, to give a more detailed account of this subject, including recent developments.