This article examines exchange across the Sierra Leone-Guinea boundary line in three different periods during the era of high imperialism. My main arguments can be summarized as follows. First, boundary crossings are best understood through a spatial analysis that combines action and structure and that emphasizes network building, power, and struggle, all shaping dynamic functional regions. Second, a multi-level analysis is needed, one that moves back and forth between the local, regional, and global, looking at how the larger forces are expressed locally in ways that influence traders’ cross-boundary strategies and at how traders helped shape structures. Third, comparing traders’ boundary crossing strategies in different time periods helps to locate the structural forces that have enhanced or reduced their adaptability - giving rise to new opportunities, or curtailing businesses. These arguments, in sum, raise questions about the relationships of traders’ actions to boundaries and to functional regions. I conclude by looking at the value of historical studies for interpreting contemporary cross-boundary trade.