Yeasts have a long tradition of application in biotechnology and a more recent history of use as research models for biochemistry, metabolism, genetics and cell biology. Without doubt, Saccharomyces cerevisiae has been the dominant representative in all these aspects. There is tremendous diversity among yeasts, however, and the application of modern microbiological and molecular approaches has resulted in renewed focus on the biology and industrial potential of other yeasts. The dairy yeast Kluyveromyces marxianus is of particular interest in this regard because of traits that render it especially suitable for industrial application. These include the fastest growth rate of any eukaryotic microbe, thermotolerance, the capacity to assimilate a wide range of sugars, secretion of lytic enzymes, and the production of ethanol by fermentation. Despite the importance of these traits, and significant exploitation by the biotechnology sector, fundamental research with K. marxianus is just emerging from the shadow of its sister species, Kluyveromyces lactis. The availability of new molecular tools and resources for K. marxianus, its interesting metabolic and cellular traits, and the potential to become the leading yeast for many biotechnological processes, argue strongly for increased research into this particular species. © 2010 The British Mycological Society.