The ubiquinol: cytochrome c oxidoreductase, or the bc 1 complex, is a key component ofboth respiratory and photosynthetic electron transfer and contributes to the formation of anelectrochemical gradient necessary for ATP synthesis. Numerous bacteria harbor a bc 1 complexcomprised of three redox-active subunits, which bear two b-type hemes, one c-type heme, andone [2Fe–2S] cluster as prosthetic groups. Photosynthetic bacteria like Rhodobacter speciesprovide powerful models for studying the function and structure of this enzyme and are beingwidely used. In recent years, extensive use of spontaneous and site-directed mutants and theirrevertants, new inhibitors, discovery of natural variants of this enzyme in various species, andengineering of novel bc 1 complexes in species amenable to genetic manipulations have providedus with a wealth of information on the mechanism of function, nature of subunit interactions,and assembly of this important enzyme. The recent resolution of the structure of variousmitochondrial bc 1 complexes in different crystallographic forms has consolidated previousfindings, added atomic-scale precision to our knowledge, and raised new issues, such as thepossible movement of the Rieske Fe–S protein subunit during Qo site catalysis. Here, studiesperformed during the last few years using bacterial bc 1 complexes are reviewed briefly andongoing investigations and future challenges of this exciting field are mentioned.