"Alpha Beta" is the story of a revolutionary idea -- that instead of using symbols to represent words, or even to represent syllables, each symbol could represent a single sound, and thereby reproduce a language in only two or three dozen symbols, rather than hundreds or thousands. John Man tracks the development of alphabets from the ancient Middle East and their spread across the world.
Man's basic theory is that the alphabet is a revolutionary idea. It is not, he says, necessarily a BETTER way to record information than syllabic/pictographic scripts, but it is certainly a different way, and one that requires a fair degree of abstraction.
He further posits that writing systems have a great deal of inertia once established, since literacy is associated with knowledge, power, and social status. Those who have put effort into learning a complicated system of writing, such as Chinese ideograms or Egyptian hieroglyphics, resist the establishment of a new system. Therefore, the alphabet is likely to have developed in fringe societies of the Middle East, those who did not want their writing to be beholden to either Egypt or the great powers of Mesopotamia, which used cuneiform writing.
Man also discusses the spread of the alphabet system, with much attention given to the development of the Latin alphabet by way of the Etruscans, Greeks, Phonecians, and probably the Hebrews. He also talks a little about the theory of alphabets and their inability to ever completely and accurately represent a language, if only because pronunciation changes. (The chapter on the Korean Hangul alphabet is particularly interesting, both in terms of alphabet design and the reluctance of the Koreans to adopt the new system over Chinese ideograms.)
Man is a little vague in places, and spends a fair amount of time spinning speculative fictions about the transmission of the alphabet through the Mediteranean. However, he is fairly careful to stress that he is only speculating, and nobody has solid evidence for much of the history of our alphabet.
In short, this is a fascinating book, and a wonderful introduction to the study of writing systems and the history of literacy. While not as in depth as I might have prefered, it does cover a vast range of time and space, and offers interesting directions for further reading.