p.xxvi line -1: "no" should be "not".

Bottom of p. 369: "covariant" should be "contravariant".

p. 550 The down arrows in the main diagram should be up, or the rows swapped.

In the first printing, on p. 554 the dates in mid page should be 1964-1965.

August 24, 2015p.319 Proposition 9.9.6 In accordance with the conventions of Chapter 13, the superscripts O and 1 in this proposition should be -, + respectively. Compare Lemma 13.7.1, which should be crossreferenced on p. 319.

October 4, 2018

p.237 Proposition 7.3.14 Replace "crossed modules" by"crossed complexes".

p.430 Exercise 12.7.8 Replace "refer forward" by "refer back". November 7, 2018 p.160 l.1 "Fig 6.3" should be "Fig 6.1" (the hyperref link is correct).

January 23, 2020 The results on classification of mappings should take account of the following paper: Topology and its Applications Volume 130, Issue 3, 15 May 2003, Pages 291-304 Topology and its Applications Compact open topology and CW homotopy type Jaka Smrekar It seems that in computing [X,Y] where X is finite dimensional CW or Y has only fiitely many nontrivial homotopy groups, then our results apply.