The ubiquity of chemicals demands new ways of thinking about human–nature assemblages. This article develops a dialogue between agrarian political economy, critical commodity chains research, and chemical geographies through a case study of the world’s most widely used agrochemical: glyphosate, commonly known as Monsanto’s Roundup. In the 1980s, glyphosate triumphed as a benign biocide that promised both safety and effectiveness. This construct made possible a capitalist agricultural assemblage characterized by chemical pervasiveness, first as a chemical replacement for mechanical tillage and since the 1990s as the chemical input for genetically modified seed packages. The ubiquity that characterizes the glyphosate assemblage is also a geography of uneven development comprising shifting firm networks, policies, and trade. Central to this assemblage since 2000, yet largely ignored, is the outsized expansion of second- and third-tier generic pesticide producers, especially in China, for whom glyphosate is part of a network entry and upgrading development strategy. Today, the glyphosate assemblage faces unprecedented challenges from weed resistance and health controversies. Whether and how the herbicide assemblage restabilizes will be determined by the complex environmental and developmental challenges of chemical agriculture and pervasive chemicals broadly, which highlights the need for a transdisciplinary dialogue that cuts across these domains.