An overview is Richard J. Hayward, “Afroasiatic,” in Bernd Heine and Derek Nurse (eds.), African Languages: An Introduction (2000), pp. 74–98. I.M. Diakonoff, Afrasian Languages, trans. from Russian (1988), is unrivaled as a historical and comparative grammar of Afro-Asiatic languages. Another valuable general resource is Joseph H. Greenberg, The Languages of Africa, 3rd ed. (1970). A challenging attempt at deep-level reconstructions is Christopher Ehret, Reconstructing Proto-Afroasiatic (Proto-Afrasian): Vowels, Tone, Consonants, and Vocabulary (1995).
Progress in the field is well documented in the proceedings (in multiple languages) of various conferences dealing with or devoted to Afro-Asiatic languages, including Dymitr Ibriszimow, Rudolf Leger, and Gerald Schmitt (eds.), Studia Chadica et Hamitosemitica (1995); Hans G. Mukarovsky (ed.), Proceedings of the Fifth International Hamito-Semitic Congress . . ., 2 vol. (1990–91); Herrmann Jungraithmayr and Walter W. Müller (eds.), Proceedings of the Fourth International Hamito-Semitic Congress . . . (1987); Ekkehard Wolff and Hilke Meyer-Bahlburg (eds.), Studies in Chadic and Afroasiatic Linguistics (1983); and James Bynon (ed.), Current Progress in Afro-Asiatic Linguistics (1984).