Proceedings of the 4th Many core Applications Research Community (MARC) Symposium In continuation of a successful series of events the 4th Many core Applications Research Community (MARC) symposium took place at the HPI in Potsdam on December 8th and 9th 2011. Over 60 researchers from different fields presented their work on many core hardware architectures their programming models and the resulting research questions for the upcoming generation of heterogeneous parallel systems.