This book constitutes the refereed proceedings of the International Conference on Multiscore Software Engineering, Performance, and Tools, MSEPT 2012, held in Prague in May/June 2012. The 9 revised papers, 4 of which are short papers were carefully reviewed and selected from 24 submissions. The papers address new work on optimization of multicore software, program analysis, and automatic parallelization. They also provide new perspectives on programming models as well as on applications of multicore systems.