As Model Driven Engineering (MDE) is increasingly applied to larger and more complex systems, the current generation of modelling and model management technologies are being pushed to their limits in terms of capacity and e ciency. As such, additional research and development is imperative in order to enable MDE to remain relevant with industrial practice and to continue delivering its widely-recognised productivity, quality, and maintainability bene ts. The third edition of the BigMDE workshop (http://www.big-mde.eu/) has been colocated with the Software Technologies: Applications and Foundations (STAF 2015) conference. BigMDE 2015 provided a forum for developers and users of modelling and model management languages and tools where to discuss di erent problems and solutions related to scalability aspects of MDE, including Working with large models Collaborative modelling (version control, collaborative editing) Transformation and validation of large models Model fragmentation and modularity mechanisms E cient model persistence and retrieval Models and model transformations on the cloud Visualization techniques for large models Many people contributed to the success of BigMDE 2015. We would like to truly acknowledge the work of all Program Committee members, and reviewers for the timely delivery of reviews and constructive discussions given the very tight review schedule. Finally, we would like to thank the authors, without whom this workshop would not exist.