Gut microbiota and its metabolic activities can influence the physiology and pathology of the human body. It is well established that alterations in the balance of living microbiota can contribute to various health problems, such as inflammatory bowel disease and autoimmune disorders. Probiotics administered in sufficient quantities as functional food ingredients provide health benefits to hosts. They help to maintain the stability and composition of the gut microbiota and provide resistance to infection by pathogens. The most important probiotic bacteria are Lactobacillus spp. and Bifidobacteria spp., which protect the intestine through various mechanisms such as the production of organic acids and bacteriocins. Scientific and clinical research has demonstrated that probiotics play a role in modulating immune response and preventing cancer and chronic inflammatory diseases, especially in the gastrointestinal tract. This article summarizes the potential health benefits, antimicrobial activities, and purposes for which probiotics can be used as functional foods to improve human health.