This chapter summarizes the knowledge of the oxidative phosphorylation (OXPHOS) constituents of Chlamydomonas and of the components involved in their biogenesis and addresses alternate dehydrogenases and oxidases which are particular to photosynthetic organisms, and several other mitochondrial components related to OXPHOS. Reference to the components of Polytomella sp., a colorless alga closely related to Chlamydomonas is clearly made. The main complexes involved in electron transport seem to share a similar number of subunits, and many of the algal polypeptides have plant homologues. Some differences are apparent, such as the presence of a fragmented COX2 subunit, which seems to be unique to chlorophyte algae. OXPHOS is defined as an electron transfer chain driven by substrate oxidation that is coupled to the synthesis of ATP through an electrochemical transmembrane gradient. The characterization of Arabidopsis mitochondrial components through proteomic approaches has advanced significantly. As a unicellular organism, Chlamydomonas offers the unique opportunity to study organelle-organelle interactions, particularly between mitochondria and chloroplasts. It has become evident that crosstalk between these organelles takes place, mainly through intracellular metabolite pools. © 2009 Elsevier Inc. All rights reserved.