Methane is an end product of anaerobic degradation of organic materials and is a potent greenhouse gas. Roughly, half of the world-wide methane emission is biologically performed by methanogenic archaea. We are interested in the enzymes involved in hydrogenotrophic methanogenesis. Here, we report on the crystal structure of the formyl-methanofuran dehydrogenase (Fwd) and heterodisulfide-reductase/hydrogenase complexes (Hdr/Mvh). These enzyme complexes are involved in the sequential reactions of ferredoxin reduction and CO2-reduction/fixation within the methanogenic pathway.