Koine Greek: The fusion of Ionian with Attic, the dialect of Athens, began the process that resulted in the creation of the first common Greek dialect, which became a lingua franca across the Eastern Mediterranean and Near East. Koine Greek can be initially traced within the armies and conquered territories of Alexander the Great and after the Hellenistic colonization of the known world, it was spoken from Egypt to the fringes of India. After the Roman conquest of Greece, an unofficial bilingualism of Greek and Latin was established in the city of Rome and Koine Greek became a first or second language in the Roman Empire. The origin of Christianity can also be traced through Koine Greek, because the Apostles used this form of the language to spread Christianity. It is also known as Hellenistic Greek, New Testament Greek, and sometimes Biblical Greek because it was the original language of the New Testament and the Old Testament was translated into the same language via the Septuagint.
Medieval Greek, also known as Byzantine Greek: the continuation of Koine Greek, up to the demise of the Byzantine Empire in the 15th century. Medieval Greek is a cover phrase for a whole continuum of different speech and writing styles, ranging from vernacular continuations of spoken Koine that were already approaching Modern Greek in many respects, to highly learned forms imitating classical Attic. Much of the written Greek that was used as the official language of the Byzantine Empire was an eclectic middle-ground variety based on the tradition of written Koine.
Modern Greek (Neo-Hellenic): Stemming from Medieval Greek, Modern Greek usages can be traced in the Byzantine period, as early as the 11th century. It is the language used by the modern Greeks, and, apart from Standard Modern Greek, there are several dialects of it.
In the modern era, the Greek language entered a state of diglossia: the coexistence of vernacular and archaizing written forms of the language. What came to be known as the Greek language question was a polarization between two competing varieties of Modern Greek: Dimotiki, the vernacular form of Modern Greek proper, and Katharevousa, meaning 'purified', a compromise between Dimotiki and Ancient Greek, which was developed in the early 19th century and was used for literary and official purposes in the newly formed Greek state. In 1976, Dimotiki was declared the official language of Greece, having incorporated features of Katharevousa and giving birth to Standard Modern Greek, which is used today for all official purposes and in education.
The distribution of major modern Greek dialect areas
The historical unity and continuing identity between the various stages of the Greek language is often emphasised. Although Greek has undergone morphological and phonological changes comparable to those seen in other languages, never since classical antiquity has its cultural, literary, and orthographic tradition been interrupted to the extent that one can speak of a new language emerging. Greek speakers today still tend to regard literary works of ancient Greek as part of their own rather than a foreign language. It is also often stated that the historical changes have been relatively slight compared with some other languages. According to one estimation, "Homeric Greek is probably closer to demotic than 12-century Middle English is to modern spoken English," (Greek has seen fewer changes in 2700 years than English has in 900 years).