We enjoy exceptional material prosperity, but its form make many of us anxious. Modern material culture appears unsustainable. And, nothing seems to epitomize this better than the proliferation of plastic. America pumps over 100 billion pounds of it into the market each year, and we have already produced more plastic in the twenty-first century than during the entirety of the twentieth. Derived mostly from fossil fuels and mostly immune from degradation, it is not surprising that many people consider plastic to symbolize unsustainability. Yet, the development of synthetic materials represents our grandparents' and great-grandparents' response to resource anxieties of their own. A hundred years ago, conservationists recognized that America's economy was overexploiting forests, fur from Canada, ivory from Africa, whale oil from the Antarctic, gutta percha from Indonesia, shellac from India, and countless other commodity feedstocks. It was in this historical context that the economic and ecological value of synthetic materials was first vindicated. Plastic's potential to relieve pressure on traditional material resources was solidified when America's burgeoning car culture compelled engineers to crack apart the hydrocarbons of crude oil to fuel more powerful internal combustion. That process produced the unsaturated hydrocarbons like ethylene that became the feedstocks of the most successful plastics. Amid material shortages of the Second World War, these new synthetics were so important that the U.S. government invested $3.5 billion into their production--$1.5 billion more than the Manhattan Project. To satisfy consumer demands of baby boomers, the Truman Administration declared that petroleum-derived materials were critical, and within a single generation America produced a greater volume of plastics that that of steel, copper, and aluminum combined. Even during the oil shocks of the 1970s, the World Watch Institute advocated for plastics given their relative energy efficiency. Plastics have functioned as a sort of get-out-of-jail-free card, sustaining our materials culture as it grew beyond the bounds of traditional natural resources. Undoubtedly, petroleum-derived plastics exacerbated certain forms of unsustainability by enabling more wasteful consumption and by deepening our reliance on petroleum. But that is only one part of the history of plastics, which is not confined to petroleum. Plastics were originally engineered from cellulose and other biological molecules, and bio-based plastics producers can capitalize on the economic and ecological benefits established by petroleum-based plastics. The complexity and scale of our economy depend on plastics. And, contrary to popular assumptions and most historiography, the history of synthetic materials I illuminate in my dissertation shows that important aspects of sustainability depend on plastics too.