In 2014 we applied Goldschmidt's concept of ionic tolerance factors to the large family of hybrid organic–inorganic perovskites. Initially seen as a guiding concept for the discovery of new hybrid organic–inorganic perovskites, the tolerance factor concept has also proven to be a valuable tool for understanding and manipulating the phase stability and properties of existing phases. Since our initial report, there have been many research examples in which tolerance factors were used to understand the existence and stability of certain hybrid organic–inorganic perovskites, while the concept itself has been continuously improved. Here we give an update on the current state of the concept, reviewing the different improvements that have been made over the past few years and drawing on topical examples in which tolerance factors have played a major role.