Publisher Summary This chapter focuses on biochemical and genetic versatility of members of the genus Rhodococcus and further emphasizes the importance of these bacteria in environmental applications. The genus Rhodococcus includes a diverse grouping within the wider group of nocardioform actinomycetes and is common in many environmental niches from soils to fresh water, seawater, plants, and animals. The remarkable ability of members of the genus Rhodococcus to degrade many organic compounds, their ability to produce surfactants, and their environmental persistence make them ideal candidates for enhancing the bioremediation of contaminated sites. With respect to their environmental significance, metabolic versatility, and potential for biotechnological applications, rhodococci are in some respects similar to the pseudomonads and related bacteria. Its genetic diversity is immense and the selection of a representative strain is difficult. A feature that can influence segregation of genetic elements, and which is often not considered, is their cellular pleomorphism.