From the reviews of the second edition: "The book under review is an introduction to the theory of categories which, as the title suggests, is addressed to the (no-nonsense) working mathematician, thus presenting the ideas and concepts of Category Theory in a broad context of mainstream examples (primarily from algebra). ... the book remains an authoritative source on the foundations of the theory and an accessible first introduction to categories. ... It is very well-written, with plenty of interesting discussions and stimulating exercises." (Ittay Weiss, MAA Reviews, July, 2014) Second Edition S.M. Lane Categories for the Working Mathematician "A very useful introduction to category theory."-INTERNATIONALE MATHEMATISCHE NACHRICHTEN