Natural gas is a broad class of gaseous fuels that derive their primary energy content from methane and are obtained from underground geological formations the same as petroleum. Methane is the fossil fuel lowest in carbon dioxide emissions when combusted. In North America and Northern Asia, it is plentiful and inexpensive, making it the preferred fuel for electric power generation, as well as domestic heating and synthesis of other hydrocarbon compounds ranging from plastics to pharmaceuticals. It is the primary feedstock for hydrogen production for ammonia fertilizer, as well as the production of hydrogen for industry and hydrogen fuel cell vehicles. It is also naturally generated by decomposition of organic materials from landfills and agriculture, and from livestock operations, and is emitted by natural gas drilling and distribution. Released into the atmosphere, it is a potent anthropogenic greenhouse gas second only to carbon dioxide as a contributor to global warming. This chapter discusses transportation-related natural gas topics, including its direct use as a transportation fuel in the form of compressed natural gas (CNG) or liquefied natural gas (LNG).