Unicellular yeast cells have been traditionally used as models of lower eukaryotic organisms and the study of yeast has made tremendous contributions to our understanding of life and cellular metabolism. In particular, the budding yeast Saccharomyces cerevisiae is the first organism whose entire genome sequence was determined. This has greatly facilitated and expedited our efforts aiming at deciphering functions of the entire genome of approximately 6200 genes. As a consequence, the functionally unknown genes have decreased from two-thirds of the genome in 1994 to less than 40% today. We are confident that in another decade, the functions of the vast majority of yeast genes will be uncovered, with new functions added to previously described genes as well.