I used this book from about pg 200 of Ulysses onward, and I think it's just about indispensable. There should not be any embarrassment in this: unless you know Latin, German, French, Hebrew (together with a good cross-section of literature from all these languages), Catholic & Jewish culture, English literature more or less entire, and (hardest of all) Dublin slang, culture, politics, and all the knick-knacks of daily life from 1904, Ulysses presents many baffling passages. This book helps out with all these things, plus plenty of other stuff: myths, songs, internal reference cross-indexing (for those of us who can't remember that Stephen Daedalus thought of the same Latin quotation 600 pages earlier), Joyce's basic scheme for each section, and more.

There are two failings, and they are minor: (1) there are still plenty of obscure words and phrases that aren't annotated (the introduction acknowledges this) and conversely (2) there are a number of things that don't need annotations that get them (particularly galling are the annotations that simply tell you that they don't know what Joyce is talking about either).

Still, an essential reference, and pretty entertaining in its own right (like flipping through an encyclopedia or Brewer's Phrase & Fable).

Ulysses Annotated is essential for understanding Joyce's seminal work, Ulysses. The Introduction, prefaces and notes explain how to use this book, and suggest why and how it was compiled. Each episode is preceeded by a map that helps the reader to visualize the movements of Bloom and Stephen throughout their journeys. It is somewhat difficult, even for a well-read student to understand Joyce's allusions without a reference guide book like Giffords.

Also recommended: REDEFINING THE 'SELF': SELECTED ESSAYS ON SWIFT, POE, PINTER, AND JOYCE by John Condon Murray

All the surface details, references to mythology, history, politics, music, literature, etc, can be found in this book (Joyce's novel is not included within, just the annotations, but it still clocks in at 700 pages!). If you want to know exactly what Joyce was referring to--this is the place. However, it won't necessarily tell you what he MEANT (aheheh, some things must be left to the reader).

Of course, if you've never read Ulysses you don't need to know every obscure reference. Just pick up REJOYCE or THE NEW BLOOMSDAY BOOK, which have generalized overviews of the novel. This is for the deep scholars. But as Joyce said, all he expects of his readers is that they study his works for the rest of their lives.

This will keep you busy.