The paper describes a flexible, problem-based approach to integrating engineering courses. Students work in teams to identify, research, and study a current problem that involves applications from each of the courses involved. Two pairs of aerospace engineering courses were used to demonstrate the feasibility and effectiveness of this idea: (a) aerodynamics and flight mechanics, and (b) compressible flow and aerospace propulsion. The courses in each pair lend themselves easily to integration because one sets the foundation for applications in the other. This approach offers undergraduates an opportunity to engage in research under the supervision of two or more faculty members, while addressing almost all the outcomes of ABET Criterion 3. It is also flexible, so it can be expanded to allow integration of material from any number of courses. The paper discusses the rationale, process, and benefits of integrating engineering courses through projects, provides specific examples of such projects, and presents a rubric for evaluating student performance.