Mucosal associated invariant T cells (MAIT) are evolutionarily old, but scientifically still quite young. The first descriptions of a human T-cell population with the canonical T-cell receptors were 25 years ago (reviewed by Lantz and Legoux1). However, it is in the last few years, since the discovery of their specificity, functionality and sheer abundance that interest has really begun to develop and spread into different fields of biology and medicine. This is part of a growing interest in innate-like or unconventional T cells which includes iNKT cells and other CD1-restricted populations, as well as subsets of gamma-delta T cells. The question of how such cells function in health and disease has developed into one of the most exciting areas in immunology, with implications from infections to cancer. This collection of seven Special Feature reviews focused on MAIT cells will help set the scene and connect some of the dots between different parts of this rapidly emerging field.