This book constitutes the thoroughly refereed post-conference proceedings of the Third International Conference on Runtime Verification, RV 2012, held in Istanbul, Turkey, in September 2012. The 25 revised full papers presented together with 3 invited papers and 2 tutorials were carefully reviewed and selected from 50 submissions. The papers address a wide range of specification languages and formalisms for traces, specification mining, program instrumentation, monitor construction techniques, logging, recording, and replay, fault detection, localization, recovery and repair, program steering...