This volume contains the conference proceedings of ISoLA 2008, the Third International Symposium on Leveraging Applications of Formal Methods, Verification and Validation, which was held in Porto Sani (Kassandra, Chalkidiki), Greece during October 13-15, 2008, sponsored by EASST and in cooperation with the IEEE Technical Committee on Complex Systems. Following the tradition of its forerunners in 2004 and 2006 in Cyprus, and the ISoLA Workshops in Greenbelt (USA) in 2005 and in Poitiers (France) in 2007, ISoLA 2008 provided a forum for developers, users, and researchers to discuss issues...