In the mid-nineteenth century, flavor additives - volatile organic chemicals with desirable aromatic qualities - began to be used to flavor sugary confections, carbonated beverages, and other mass-marketed delights. By the mid-twentieth century, added flavors had become ubiquitous in processed, packaged foods; a sophisticated, technoscientific, and globe-spanning industry had emerged that specialized in their production. Drawing on history of science and technology, business history, and cultural history, "Flavor Added" investigates the history of synthetic flavor additives, the systems of scientific and technical knowledge that emerged to create these substances, and their social and cultural consequences. Focusing primarily on the United States, "Flavor Added" traces the origins and development of both flavor chemistry and sensory science, illuminating their entangled roots in private industry, regulatory laboratories, USDA research experiment stations, the US military, and academic institutions. Several chapters take on the technologies and tools of flavor creation, including the taste panel, the flavor profile, and the combined gas chromatograph-mass spectrometer. This dissertation also documents the professional history of flavorists, the highly specialized scientific craft-workers who develop and design flavor additives.