Even before American involvement in World War I, motor vehicle manufacturing in the United States was widespread and diverse, though the war served to expand the market rapidly. Hundreds of companies were building vehicles for military as well as civilian use during this time. From their beginnings until their demise, the histories of 225 companies that manufactured cars, trucks or motorcycles for the civilian market are provided, along with illustrations and specs of representative models from each company that existed in 1917 and 1918.