Probiotics are live microorganisms that, when consumed in adequate amounts, confer health benefits beyond basic nutrition. They are primarily lactic acid bacteria, such as lactobacilli, enterococci, and bifidobacteria, which have been used for their health-promoting properties. Probiotics are increasingly recognized for their ability to alleviate symptoms of lactose intolerance and shorten the duration of rotavirus-induced diarrhea. They also show promise in the prevention and treatment of atopic diseases. However, many proposed health effects require further investigation, especially regarding their benefits for healthy individuals, the main market for probiotics. Additionally, the potential use of probiotics outside the gastrointestinal tract needs more exploration. The definition of probiotics has evolved, with some studies suggesting that inactivated probiotic microorganisms or their components may also have beneficial effects. This has led to new definitions and a broader understanding of probiotics. The choice of probiotic microorganisms depends on various factors, including their ability to survive the gastrointestinal tract, their ability to adhere to the intestinal mucosa, and their capacity to modulate the immune system. Probiotics are typically administered through fermented dairy products, but other microbes and even yeasts are being explored as potential probiotics. Clinical studies are essential to establish the health benefits of probiotics and to support their use in the prevention and treatment of specific diseases.Probiotics are live microorganisms that, when consumed in adequate amounts, confer health benefits beyond basic nutrition. They are primarily lactic acid bacteria, such as lactobacilli, enterococci, and bifidobacteria, which have been used for their health-promoting properties. Probiotics are increasingly recognized for their ability to alleviate symptoms of lactose intolerance and shorten the duration of rotavirus-induced diarrhea. They also show promise in the prevention and treatment of atopic diseases. However, many proposed health effects require further investigation, especially regarding their benefits for healthy individuals, the main market for probiotics. Additionally, the potential use of probiotics outside the gastrointestinal tract needs more exploration. The definition of probiotics has evolved, with some studies suggesting that inactivated probiotic microorganisms or their components may also have beneficial effects. This has led to new definitions and a broader understanding of probiotics. The choice of probiotic microorganisms depends on various factors, including their ability to survive the gastrointestinal tract, their ability to adhere to the intestinal mucosa, and their capacity to modulate the immune system. Probiotics are typically administered through fermented dairy products, but other microbes and even yeasts are being explored as potential probiotics. Clinical studies are essential to establish the health benefits of probiotics and to support their use in the prevention and treatment of specific diseases.