While several “grand narratives” have been developed to account for the impact of scientific things on scientific practice, there is still very little methodological support for comparative analyses of scientific things. The goal of our article is to sketch the methodological challenges involved in comparatively analyzing scientific things and including their properties in middle-range theories of scientific practice. Methodological challenges arise from the necessity to use scientists' accounts of scientific things, the dilemma between depth and breadth of comparative case-study approaches, and from the necessity to compare accounts of scientific things to each other as well as to social conditions of research. Since the dominant approaches to the study of scientific things avoid the middle levels of abstraction, we suggest using an approach based on a theory of action. Two examples from a recent study of conditions for scientific innovations illustrate our approach to the comparative analysis of properties of scientific things.