A review is provided on the aqueous reduction of CO2 to hydrocarbons at copper electrodes, covering the literature since the first report of the reaction in 1985. This reaction is of interest as a potential component of a carbon energy cycle (i.e. CO2 +energy→methane→CO2 +energy). The synthesis of hydrocarbons from CO2 is a complex multistep reaction with adsorbed intermediates, most notably adsorbed CO. The exact reaction mechanisms leading to the various products are not clear from the literature data to date and likely change over the range of conditions at which data has been reported. The reaction product distribution is also very sensitive the surface crystal structure copper electrode. The influences of various reaction conditions (potential, buffer strength and local pH, local CO2 concentration, stirring, and CO2 pressure) are discussed and some relationships between reaction conditions and products formed are presented.