The microalgae Chlorella spp., Dunaliella spp., and Scenedesmus spp., and the cyanobacteria Spirulina spp., and Aphanizomenon flos-aquae, are being used as nutrient-dense foods and sources of fine chemicals. They have significant amounts of lipid, protein, chlorophyll, carotenoids, vitamins, minerals, and unique pigments. They may also have potent probiotic compounds that enhance health. Their historical and current use are reviewed in this article.