The positive impacts of prebiotics and probiotics on the gastrointestinal (GI) health of human adults have been known for many years. However, their effects on newborns and infants have not yet been analyzed in detail. Many processed baby foods are now enriched with probiotics, a live microbial food supplement that benefits the host by improving the microbial balance of the intestine. A more recent development has been the inclusion of prebiotics which has been observed to effectively promote the growth of specific gut microflora such as Bifidobacterium. However, a major issue encountered has been the survival of the organisms contained in the supplements both before ingestion, and afterwards on their way to the target organ, the gut. Synbiotics have been seen as a potential solution to this problem. Several studies have shown that probiotics and prebiotics can help to prevent infections in the GI tract of infants and also strengthen their immune system. This could make a huge difference to infants who have been bottle-fed and thus not provided with the probiotics they would normally have received from breast milk. This chapter describes the effects of pre- and probiotic supplements in detail, as well as their mechanisms of action, and also attempts to analyze their possible health benefits to infants.