The Mythical Man-Month: Essays on Software Engineering is a classic book on software engineering, written by Frederick P. Brooks to pass on some of the insights he had gained from managing development of OS/360. Its novel observation was that, unlike some other types of engineering problems, when a project falls behind schedule it doesn't work to add more people. The impact of this observation was so significant that the term "mythical man-month" became a part of the computing lexicon.

Other significant contributions include a description of the second-system effect, and advocacy of prototyping, summed up in the advice "plan to throw one away".

The book was first published in 1975, and republished virtually unchanged (just an addition of a chapter) 20 years later.