This essay seeks to initiate a discussion of the problem of scale among social scientists. Long familiar to natural scientists, the problem of scale centers on the transferability of propositions from one level to another in the dimensions of space and time. As a means of pursuing this goal, the essay examines similarities and differences between studies of micro-level institutions (common-pool resource [CPR] arrangements) and macro-level institutions (international resource regimes) governing human/environment relations. The conclusions are mixed. Some concerns (for example, the importance of transparency) loom large at both the micro level and the macro level. But others (for instance, the role of culture in connection with CPRs and the centrality of domestic implementation in connection with international resource regimes) are relevant primarily to one or the other level of analysis.