Cambridge English Pronouncing Dictionary

The first 14 editions of the EPD covered only British English. The 15th edition (1997), published by Cambridge University Press and edited by Peter Roach, James Hartman and Jane Setter, introduced American pronunciations. The changes in the 16th edition (2003) were relatively small — new words and over 150 "information panels" explaining phonetics terminology. The 17th edition (2006) has continued the slow evolution, with the addition of further words and a "Study pages" section with a very brief introduction to English pronunciation, rhythm and intonation.

Why is a pronunciation dictionary useful?

Here are the advantages of a specialized pronunciation dictionary, such as the EPD, over a general dictionary with definitions of words:

More words. A pronunciation dictionary can list pronunciations for more words than a general dictionary. It can include first names, last names, geographical names, company names, trademarks, etc.
Word forms. It can give the pronunciations for inflected forms of words — e.g. starts, started, starting — not only for the main form like start. This is especially helpful for beginner learners, who can learn that e.g. goes ends in z, not s.
More pronunciation variants. A pronunciation dictionary can list more ways to pronounce the same word. Specifically, it can explain how to pronounce a word in a sentence. For instance, and is pronounced /ćnd/, but "and all" may be pronounced /?n '?:l/.
More precise transcriptions. It can use additional symbols to give more detailed information on pronunciation.
More authority. We can expect that a pronunciation dictionary will contain fewer errors in transcriptions than a general dictionary.
Whose pronunciation is covered?

An important question about any pronunciation dictionary is "Whose pronunciation is represented?". The EPD answers this question in its well-written introduction.

For British English, the EPD follows the pronunciation of those newsreaders on BBC radio and television who speak with an English accent (rather than Scottish, Welsh or Irish). The authors call this model "BBC English", but it is really a modern version of RP.
For American English, the EPD follows the accent of professional voices on news and information programs on American national TV networks (such as CNN, ABC, NBC, CBS or FOX). This model is called "Network English" (why not "General American"?).
This definition of pronunciation models makes a lot of sense. Almost all speakers of English watch TV, therefore the "TV accents" are very understandable. They are also the easiest to learn, because television networks like BBC World or CNN International are widely available and the sound quality on TV is excellent.