Developmental evaluation (DE) is an early 21st century development, so it is altogether fitting that its state of development be reviewed at the AEA annual conference. DE applies systems thinking and complexity concepts to evaluation of social innovations. Evaluation in complex dynamic systems requires nimble adaptation, timely feedback, and special attention to phenomena like emergence, nonlinearity, and dynamical changes. As the author of the primary book on DE and as a regular trainer in DE, I receive reports from practitioners about the challenges they are facing and questions they are struggling with. This session will address those emergent issues and challenges with special attention to how to design and budget for developmental evaluations given the emergent and dynamic nature of DE, how to deal with the potentially overwhelming amount of data that can be collected to document rapid changes, and how to manage relationships with social innovators and funders, among others. Examples of actual DE projects will be featured.