Electrofuels is a newly created biofuel technology concept that may have significant potential in producing transportation fuel from non-biomass feedstocks such as CO2, H2 and/or electricity. One of its key features is the application of certain chemolithoautotrophic organisms with synthetic biology to synthesize biofuel(s), such as butanol through fixation of CO2 using H2 and/or electrons as a source of reductant. Potentially, this approach could become quite attractive for biofuels pro­duction, since large quantities of inexpensive electricity (thus H2 from electrolysis of water) and CO2 feedstock could foreseeably become available in the near future. With advanced photovoltaic cells, the solar-to-electricity energy conversion efficiency can now reach more than 20%. A solar electricity-based electrofuel process with certain chemolithoautotrophic CO2 fixation pathways [21] could have a combined solar-to-biofuels energy conversion efficiency higher than that of a photosynthesis-based biofuel technology. Therefore, the electrofuels approach merits serious exploration also. In 2009, the United States Department of Energy (DOE) Advanced Research Projects Agency-Energy (ARPA-E) created the electrofuels program to explore the potential of non-photosynthetic autotrophic organisms for the conversion of durable forms of energy to energy-dense, infrastructure-compatible liquid fuels. Chapter 38 reports the US DOE/ARPA-E Electrofuels program efforts, including its rationale, approach, potential benefits, and challenges. Chapter 39 dis­cusses the motivations and the methods used to engineer Ralstonia eutropha to pro­duce the liquid transportation fuel isobutanol from CO2, H2, and O2; and Chap. 40 reports the development of an integrated Microbial-ElectroCatalytic (MEC) system consisting of R. eutropha as a chemolithoautotrophic host for metabolic engineering coupled to a small-molecule electrocatalyst for the production of biofuels from CO2 and H2, which extends well beyond biomass-derived substrates.