This book constitutes the thoroughly refereed post-proceedings of the 11th International Workshop on Coalgebraic Methods in Computer Science, CMCS 2012, colocated with ETAPS 2012, held in Tallin, Estonia, in March/April 2012. The 10 revised full papers were carefully reviewed and selected from 23 submissions. Also included are three invited talks. The papers cover a wide range of topics in the theory, logics and applications of coalgebras.