This volume contains the proceedings of the Third International Symposium on Games, Automata, Logic and Formal Verification (GandALF), held in Naples (Italy) from September 6th to 8th, 2012. GandALF was founded by a number of Italian computer scientists interested in mathematical logic, automata theory, game theory, and their applications to the specification, design, and verification of complex systems. Its aim is to provide a forum where people from different areas, and possibly with different backgrounds, can fruitfully interact. Even though the idea of the symposium emerged within the Italian research community, the event has a truly international nature, as witnessed by the composition of the conference committees and the programme.