Work is frequently interrupted. What is known about how interruptions affect productivity? This important question has been studied using a variety of research methods, from controlled experiments designed to learn about the effect of interruptions on task performance, to analytical cognitive models that explain what makes an interruption disruptive, to in-situ observational studies that document the kinds of interruptions people experience in their actual workplaces. In this chapter, we review research on interruptions that has used these three research methods. We review what the methods entail, and what insights it has given on how interruptions affect productivity.