Yeasts are single-celled micro-organisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constitute 1% of all described fungal species.

See: Yeast, biodiversity of. | Yeast biotechnology. | Yeast classification. | Yeast, economic significance of. | Yeast hulls. | Yeast inoculation. | Yeast, origins of. | Yeast, wild is more complex. | Wasps (for their role in the evolution of natural populations of Saccharomyces cerevisiae, the main strain of yeast used in winemaking).