益生菌（Probiotics）是指可改善宿主（如动物或人类）肠内微生态的平衡，并对宿主有正面效益的活性微生物。

益生菌（Probiotics），源于希腊语「for life」（对生命有益），中文译为「益生菌」或「原生保健性菌种」，为科学家经研究证实后，于1965年，Lilly and Stillwell将益生菌定义为：「任何可以促进肠道菌种平衡，增加宿主健康效益的活的微生物」。经过科学家四十多年来的研究，有些益生菌的功效比原先的定义更为广泛；而益生菌主要是指乳酸菌和部分酵母菌。 初步科学临床实验数据显示:益生菌的补充或有助于免疫系统、肠道健康、预防癌症等健康支持作用.

Probiotics are microorganisms that are believed to provide health benefits when consumed. The term probiotic is currently used to name ingested microorganisms associated with benefits for humans and animals. The term came into more common use after 1980. The introduction of the concept is generally attributed to Nobel recipient Élie Metchnikoff, who postulated that yogurt consuming Bulgarian peasants lived longer lives because this custom. He suggested in 1907 that "the dependence of the intestinal microbes on the food makes it possible to adopt measures to modify the flora in our bodies and to replace the harmful microbes by useful microbes". A significant expansion of the potential market for probiotics has led to higher requirements for scientific substantiation of putative benefits conferred by the microorganisms.