Course of illness, treatment effectiveness, and outcomes in bipolar disorder are studied in various ways, including randomized controlled clinical and pragmatic trials and observational studies. Clinical trials have important limitations that often make the application of findings difficult in real-world settings. Pragmatic trials study a treatment intervention in a more practical setting, but recent pragmatic trials of bipolar disorder treatment have yielded disappointing results. Observational studies can complement randomized trials because they provide valuable insight into the course, treatment response, and outcomes of patients who would generally be excluded from clinical trials.