Probiotics represent a powerful strategy to sustain health via dietary supplementation. Commonly used microorganisms include members of the Lactobacillus, Bifidobacterium, and Saccharomyces genera. Trials substantiate probiotic use for the maintenance of homeostasis and disease prevention across the lifespan, including the prevention of various forms of diarrhea or reducing the risk of upper respiratory tract infections. Additionally, selected probiotics may be useful for disease management, such as in pouchitis or Helicobacter pylori infection. Pre-clinical and clinical research demonstrates common mechanisms of action across multiple probiotics, in particular explaining their role in pathogen exclusion and supporting eubiosis. Species- or strain-specific mechanisms also exist for selected benefits such as immunomodulation. For inclusion in supplements, probiotics need to be characterized and tested in adequate trials supporting the specific benefit associated with the specific product tested. This will support informed consumer choices as well as appropriate manufacturing.