The central aim of The Philosopher's Dictionary is to provide a comprehensive and up-to-date guide of philosophical terms. Definitions are brief, clear, and user-friendly. Notes on usage, spelling, and pronunciation are included, and there are brief entries on hundreds of the best-known philosophers. Throughout, Martin writes in a style at once informative and authoritative, making difficult concepts intelligible without distorting them.

The third edition has been revised throughout, and includes many new entries on philosophical concepts, from Berry's paradox to the Chinese room example to perfectionism and satisfice. The number of entries on active philosophers has also been considerably increased.