Mark Morris avoids biography almost entirely in this excellent dictionary, concerning himself only with detailed musical analysis and discussion. There are entries on over 500 composers, many of which are substantial. The dictionary is arranged by country - each country gets a short introductory essay, followed by entries on individual composers with lists of recommended works. Morris, a Welsh writer and librettist, is unashamedly frank in his musical analyses.
Of Philip Glass he remarks: "At his worst (which is often), his music can be horrendously banal and infuriatingly trite." He doesn't try to be too up-to-date, including only composers who are well established. One error: Ireland is given a cursory entry in the book, under Eire, but is omitted from the countries index. Overall, Twentieth-Century Composers should prove of value to both layman and expert.