Geoffrey Horrocks' GREEK: A History of the Language and its Speakers is the first English-language overview of the entire span of Greek history (Homer to contemporary Modern Greek) based on the recent integration of sociolinguistics and historical linguistics. That means that the history of Greek is not any single variety being replaced by another single variety, but rather a constant flow of registers and conscious attempts to reform the language back to this or that classical style. Abundant selections from both literary Greek and personal correspondence show these different and ceaselessly evolving styles.
I was a bit disappointed that, unlike in the recent Blackwell History of Latin that he wrote with James Clackson, Horrocks does not begin with Proto-Indo-European. Indeed, even Proto-Greek gets little attention, and the history really chooses the Ionic style of Homer as the beginning of the Greek language as it has lasted up until today.
The work requires knowledge of at least Classical Greek--I can't imagine the reader getting anything out of it otherwise. Each passage is, however, glossed word-for-word, with phonetic transcription. By doing this Horrocks shows the changing pronunciation of Greek through time even though the Greek script often remains the same.
My only experience with Greek is reading Classics as an undergraduate. I've always been intrigued by the modern language, which is always hyped as so much close to the classical language than the Romance languages are to Latin, and Horrock's presentation of the grammatical and lexical changes that produced contemporary spoken Greek were entertaining reading. However, Horrocks presents everything in a theoretical fashion, and people with training in Classical Greek who want to quickly achieve actual spoken proficiency in the modern language should look to: Kavoukopoulos, F., Omatos, O., Stavrianopulu, P., Alonso, J., Madariaga, E. _Griego Moderno para Filólogos Clásicos_. Dos volúmenes, dos cassettes y CD. Universidad de Creta – Universidad del País Vasco. Ed. Nefeli. Atenas, 1999. Pp. (Volumen I, pp. 331. Volumen II, pp. 275).