Cheese whey, the main dairy by-product, is increasingly recognized as a source of many bioactive valuable
compounds. Nevertheless, the most abundant component in whey is lactose (ca. 5% w/v), which represents a
significant environmental problem. Due to the large lactose surplus generated, its conversion to bio-ethanol
has long been considered as a possible solution for whey bioremediation. In this review, fermentation of lactose
to ethanol is discussed, focusing on wild lactose-fermenting yeasts, particularly Kluyveromyces marxianus, and
recombinant Saccharomyces cerevisiae strains. The early efforts in the screening and characterization of the
fermentation properties of wild lactose-consuming yeasts are reviewed. Furthermore, emphasis is given on the
latter advances in engineering S. cerevisiae strains for efficient whey-to-ethanol bioprocesses. Examples of
industrial implementation are briefly discussed, illustrating the viability of whey-to-ethanol systems. Current
developments on strain engineering together with the growing market for biofuels will likely boost the
industrial interest in such processes.