We describe efficient algorithms for finding even cycles in undirected graphs. Our main results are the following: (i) For every k 2, there is an O(V 2) time algorithm that decides whether an undirected graph G = (V, E) contains a simple cycle of length 2k, and finds one if it does. (ii) There is an O(V 2) time algorithm that finds a shortest even cycle in an undirected graph G = (V, E). Key words. graph algorithms, cycles AMS subject classifications. 05C85, 05C38, 68R10 PII. S0895480194274133