On November 4, 1879, Thomas Edison filed for a patent for an electric lamp using carbon filaments. Edison’s patent, which became the first commercially successful, long-lasting light bulb, changed the way people across the world live and work—with the flip of a switch. Soon, electricity became a business in and of itself, with Edison and the American engineering mogul George Westinghouse bringing electric power to cities across America. Supported by innovative scientists and engineers like Nikola Tesla, this booming new industry shaped twentieth-century American culture and industry. This primary source set explores the development, commercialization, and impact of electricity.