Hi, Dave! Consider this book: *Basic Category Theory for Computer Scientists (Foundations of Computing)http://www.amazon.com/Category-Computer-Scientists-Foundations-Computing/dp/...-- *Benjamin C.Pierce This is at the moment the only book about category theory I've read, but it was easy for me as for programmer rather than mathematician to understand most of the stuff. Now I am reading "Categories for the Working Mathematician" and just can't go further 50-60 pages, cause for understanding rest of the book I must understand examples given in the book, and those are mainly from group theory, topology and functional analysis. As I am slightly familiar with any, first I need to learn some other mathematics. So if you are rather programmer than mathematician, I think you'd better start with book I mentioned above. Otherwise you should stock up with lots of books about less abstract mathematics =) With best regards, Nick