Abstract: Probiotics are health promoting viable microorganisms which have useful effects on the health of digestive system when acquired in a defined dosage. Probiotics can be formulated in to different types of products like food, drugs and dietary supplements. Probiotics improve digestion of food, absorption of nutrients, reducing cholesterol levels, pharmaceuticals development, functional food development and preventing growth of undesirable microorganisms in the digestive tract. The selection of probiotics from different sources involving the evaluation of the basic features of these bacteria, including acid, salt and bile tolerance, ability to adhere to the gut, combat pathogens in the GIT, production of antimicrobial substances, ability to stimulate the response and ability to influence the metabolic activities. Potential probiotics has been isolated from human sources such as feces of healthy adults, breast fed infants and human breast milk and animal sources are poultry, pigs and ruminants. Probiotic bacteria isolated from these sources like Enterococcus faecalis, L. salivarius, L. rhamnosus and L. casei helps to improve human health particularly today with the increasing threat of antibiotic over usage and the prevalence of antibiotic resistance organisms. The use of growth promoting antibiotics in animal feeds is banded in different countries due to potential risks such as the spread of resistance genes and the contamination of milk and meat with antibiotic residues. As a result, many livestock producers and researches have explored different alternative strategies to enhance animal performance and health. Probiotics are one of the best alternatives to improve animal production. The use of probiotics in animals improves milk production in lactating cows, milk fat, milk protein and SNF contents. Safety is an overarching concern among all probiotic stakeholders, from government regulatory agencies, to consumer advocacy organizations, to manufacturers. However, still there are not systematic reviews that analyze adverse effects and safety of probiotic administration evidence to date has demonstrated no serious adverse effects. The market of probiotics in global market is rapidly increased. The market in 2015 was $33.19 billion and expected to reach $46.55 billion by 2020 which indicates a compound annual growth rate of 7%.