Chapter 27 considers state-and-transition models (STMs), which are tools to explain the causes and consequences of ecosystem change. The chapter discusses general types of STMs, including conceptual STMs, spatial and non-spatial state-and-transition simulation models, process-based STMs and ecosystem service-based STMs. It goes on to discuss the types of social-ecological systems (SES) problems and research questions commonly addressed by this set of methods, as well as their limitations, resource implications and new emerging research directions. The chapter also includes an in-depth case study showcasing the application of STMs, and suggested further readings on these methods.