This year, deciding which paper should receive the best paper award at the 4th Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS 2011) was a difficult task for the Program Committee. After much deliberation the committee decided that the Rapita Systems Award and €200 prize for best paper should go to Marcelo Santos, Björn Lisper, Veronica Lima and George Lima for their paper on ‘Sequential Composition Of Execution Time Distributions By Convolution’. With over 30 participants, the 4th Workshop on Compositional Theory and Technology for Real-Time Embedded Systems in Vienna (29th Nov 2011) was described by co-chair Rob Davis of Rapita Systems and the University of York as “an outstanding success”. “Francisco Cazorla from Barcelona Supercomputing Centre gave an excellent keynote presentation on ‘Time Composable Multicore Processors For Critical Real-Time Embedded Systems’ which provoked a lively question and answer session. This was followed by presentations of six workshop papers, all of which were of a very high standard”. The 4th Workshop on Compositional Theory and Technology for Real-Time Embedded Systems (CRTS) was held in Vienna on 29th November 2011. The proceedings and workshop presentations are available on the CRTS 2011 website: http://www.rapitasystems.com/crts2011/