Primary producers are known to utilize six pathways for CO2 fixation, which represent billions of years of evolution and optimization for survival and reproduction of the host organisms (Table ). Humans and all other organisms are dependent on these primary producers to derive organic carbon to sustain life on this planet. Because these CO2 fixing pathways are central to the existence of life, prior research efforts focused on better understanding these biological systems have been useful starting points to capture and sequester atmospheric CO2. 12, 15, 97-100 ￼ Among the six CO2 fixation pathways, the reductive pentose phosphate pathway or the Calvin-Benson-Bassham (CBB) cycle is by far the prevalent mechanism used by all plants and algae, and most autotrophic bacteria for converting atmospheric CO2 into biomass. It is also the most economically relevant pathway. The other five pathways are only present in a small number of bacteria or archaea, but nevertheless provide clues regarding the unique environments in which the host organisms thrive. Recent efforts include engineering natural CO2 fixation pathways in nonnative organisms, 103-109 and engineering synthetic CO2 fixation pathways into organisms. An emerging new concept combines microbial or algal cell factories with electrochemistry to directly convert CO2 Each approach represents a promising line of investigation potentially leading to the capture of gigaton quantities of CO2 from the atmosphere using natural biological hosts.