This volume contains the proceedings of the ThirdInternational Conference on Deductive and Object-OrientedDatabases. Its central tenet is that the object-oriented anddeductive paradigms for modeling, organizing, and processingdata complement each other, rather than competing, and thatproblems involving massive volumes of complex data can bestbe solved by integrating the best of both approaches. Central questions in the area are:- How do we design a tool that presents the best of theobject-oriented and declarative ideas?- How can the users of this tool express their problems in acombination of declarative and procedural features? The volume includes 29 papers that contribute towardsanswering these questions.