In ecology and evolution, we often encounter problems where we want to use particular nonlinear functions or response distributions that can’t be simplified for use in linear or generalized mixed models: for example, functional response curves in predator-prey systems or von Mises distributions for turning angles in animal movement. This master class will cover typical uses of general nonlinear maximum likelihood estimation in R. We’ll start with a *brief* review of maximum likelihood theory and of nonlinear optimization, then go through practical examples – mostly using the bbmle package and focusing on troubleshooting the many technical problems that can occur in real-life problems. We will touch on the challenges of combining mixed models with general nonlinear estimation.