In a wonderful succinct article written 35 years ago Peter Evans identified the crucial structural/relational insight of world-system analysis that claims a "single ongoing division of labor.based on differential appropriation of surplus produced [such that] positions are hierarchically ordered, not just differentiated" (1979:15-16). Later we summarized a major theme of the paradigm: a "country's world system position, in a macro-structural sense, is considered a key determinant of the society's capacity for sustained economic growth and development" (Crowly, Rauch, Seagrave and Smith 1998: 32). The key hypothesis is that if a scholar knows where a country or region "fits" in that hierarchy, one should also be able to predict various developmental outcomes - and the core/semi-periphery/periphery stratification should also align with various sorts of international/global inequalities. A vexing issue becomes how to shift and sort places into the strata. In the seminal writings of Immanuel Wallerstein, these are historically defined, based on "unequal exchange" in 15th century Europe that led to a continentand later world-wide division of labor reliant on long-distance trade. For him, the semi-periphery (SP) takes on a key political role as a "buffer zone" between the core/periphery - but it's defined by its economic role. Christopher Chase-Dunn (1998), argues that SP countries contain "a relatively equal mix of core and peripheral types of production" (77) or "a predominance of activities which are at the intermediate levels with regard to the current world-system distribution of capital intensive/labor intensive production" (212). This "middling" level in terms of forces of production means that the SP strata simultaneously has a global competitive edge over the core in terms of lower labor costs and an advantage over the periphery via its existing economic base (infrastructure, human and other forms of capital) to implement advanced production processes. A portion of my own empirical research over the decades takes focuses on attempting to empirically capture the relational aspect of the international division of labor via quantitative network analysis that attempts to "model" the worldsystem, examining international commodity trade between nation states. In this paper, I will draw on the most recent attempt to do that (Mahutga and Smith 2011), which provides a recent data-driven "sorting" of countries into core/semi-periphery/periphery - and also examines that global structure over time (from 1965-2000), permitting some discussion of which countries are "mobile"/"moving up" as we moved into the current century. But this essay will use the empirics of that analysis as a starting point, and focus on central questions about social change in the 21st century. Are the BRICS best considered S-P, more emerging core states? Where does China "fit"? Are the peripheral states of Europe S-Ps? In attempting to answer some of these questions, I hope to return to some basic issues about what "semi-peripherality" might mean in the future, how it is different from the past, and whether it is still relevant as a category. [ABSTRACT FROM AUTHOR]