Protoplast fusion has made a significant contribution to our understanding of the genetics and biochemistry of the nonconventional yeasts, and it has facilitated the creation of novel strains of yeast that display enhanced biotechnological potential. This article presents an examination of the means of isolating, reverting, and fusing yeast protoplasts, as well as an analysis of the products resulting from such fusions. Although this review is primarily concerned with the impact protoplast fusion has made on our knowledge of the nonconventional yeasts, where appropriate, reference to data gained from work with the conventional yeasts, i.e., Saccharomyces or Schizosaccharomyces, is made.