Abstract Reactors are vessels employed to carry out transformations from one chemical to another. When the substrate (chemical) or feedstock is biobased, or the transformation is catalyzed by microorganisms and/or enzymes, the reactor is also termed a bioreactor. In this article, we focus on bioreactors employed in sustainable chemical and/or energy conversions. Since there are numerous sources and texts dealing with reactor designs, the objective of this article is to explain the special features of various sustainable bioreactors without going into the details of the reactor design.