As science studies scholars, one of our basic tasks is to draw the boundaries that will define our units of inquiry and constrain the chronological and geographical limits of our studies. Without these boundaries, the categories of our analysis remain imprecise. Fortunately, we now have an extensive toolkit to help us with this task. With paradigms, research programs, epistemic cultures, or styles of reasoning, historians, philosophers, and sociologists of science now have a large set of resources for locating the fissures and discontinuities in science. The papers from the focused discussion of this issue of Spontaneous Generations present us with an opportunity to take a step back and examine the ways that science studies scholars are currently drawing boundaries. In reviewing the articles for this discussion, our aim as editors was to reflect on what boundaries scholars were paying attention to and what use we can make of these boundaries.