In its roughly 130-year existence, the automobile has played a major role in altering the atmospheric composition of the planet, most notably from the carbon dioxide (CO2) generated by the combustion engines that power them, but also from every step of the extraction, refining, and distribution of fossil fuels. Transportation, including land, sea, and air, has been a major contributor to the greenhouse gas (GHG) CO2 that is now known to be primarily responsible for global warming. And within the entire field of transportation, passenger cars produce the largest share of CO2 emissions. This chapter reviews the environmental impacts of automotive transportation and demonstrates that different fuels have characteristically different GHG and regulated emissions. Calculation of the comparative CO2 emissions per energy content for various fuels and electricity sources is covered. Regulatory advances and missteps, and counterproductive solutions are discussed, and finally a look back at progress from the late twentieth century.