This book is a collection of the papers presented at the 33rd Communicating Process Architecture (CPA) conference, held at the University of Limerick, Ireland, 19-22 June, 2011. It was hosted by Lero, the Irish Software Engineering Research Centre, and co-located with FM 2011 (the 17th International Symposium on Formal Methods), SEW-34 (the 34th Annual IEEE Software Engineering Workshop) and several specialist workshops and tutorials. These CPA proceedings contain the results from rich seams of research covering many of the key issues in modern computer science, which all seem to concern concu.