How do people solve big problems with small brains? My research tries to answer this question through the lens of adaptative computation. People use cognitive strategies that are well-suited to both their external environments and their internal computational constraints. I characterize these strategies using AI theory (like reinforcement learning and metareasoning) and process-tracing experiments (like eye- and mouse-tracking). I also study how and why cognitive strategies go awry (e.g., in mental illness) and what we can do to help people think in more productive ways.