I have written this article primarily as an overview for students who are studying Greek at A level and beyond; it may also be useful for their teachers. It covers the period from the Archaic age up to the beginning of Medieval Greek (c. 750 BCE to 500 CE). There is an emphasis on Classical Greek both within and beyond the Classical period, since the Classical form, or approximations to it, has never ceased to be learned, the only form of Greek of which this can be said. It has also left a sizeable imprint on Modern Greek, especially but not exclusively on its more educated forms. I hope though that the article will serve to draw the users’ attention to the many other forms of the language apart from Classical Greek. I know that I could have done with something like this when I was a student: I was hardly aware of the existence of the κοινή, except perhaps as a form of Greek used by Christian writers long after the end of the Classical period.