This volume contains the proceedings of the Third International Conference on Deductive and Object-Oriented Databases. Its central tenet is that the object-oriented and deductive paradigms for modeling, organizing, and processing data complement each other, rather than competing, and that problems involving massive volumes of complex data can best be 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 the object-oriented and declarative ideas? - How can the users of this tool express their problems in a combination of declarative and procedural features? The volume includes 29 papers that contribute towards answering these questions.