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 and adaptation, metrics and statistical information gathering, combination of static and dynamic analyses and program execution visualization.