Probiotics are an important topic in food microbiology. They are defined as live microorganisms that can provide a health benefit to the host when consumed in adequate amounts, provided that scientific evidence supports the specific benefit of the strain used. Some of these microorganisms are found in fermented food products, while others are added to foods formulated to deliver specific microbial strains. However, the presence of live bacteria in a food product does not automatically mean that the product qualifies as a probiotic. Microorganisms used in certain probiotic products include strains of lactic acid bacteria, such as species of Lactobacillus, as well as species belonging to the genus Bifidobacterium. These strains differ in their ability to tolerate acidity and bile salts, as well as their capacity to survive food processing, storage, and passage through the digestive tract. Therefore, strain identification, viability assessment, and safety verification are essential steps in the development of probiotic products. Several potential mechanisms underlying the effects of these microorganisms are being investigated. These include competing with certain microbes for nutrients and adhesion sites, producing organic acids or compounds that inhibit specific microorganisms, and interacting with the intestinal barrier and immune system. Some strains may also influence the activity of the intestinal microbial community or the production of certain metabolic compounds. However, these effects vary among strains, individuals, and products. Findings from research conducted on a specific strain should not be generalized to all beneficial bacteria. In food manufacturing, the viability of probiotic strains must be maintained throughout production, packaging, transportation, and storage. The number of viable cells may be affected by temperature, acidity, oxygen exposure, product composition, and storage duration. Accordingly, appropriate processing and packaging technologies are used, and microorganisms may be added at a stage that helps ensure they remain at the required levels until the end of the product's shelf life. It is also important to distinguish between fermented foods and probiotic foods. Fermented foods may contain live microorganisms, but not all of them qualify as probiotic products in the scientific sense. This classification requires identifying the microorganism used and demonstrating its health benefits. The safety of the strains must also be assessed, taking into account the nature of the product and the intended consumer group. The study of probiotics connects food microbiology with nutrition and the microbiome, helping researchers understand how to develop foods with specific functional properties. It also emphasizes the importance of scientific evidence, manufacturing quality, and avoiding exaggerated health claims. Al-Mustaqbal University – The First University in Iraq