Prebiotics and probiotics have attracted considerable interest as alternatives or replacements for growth-promoting antibiotics and/or some heavy metals in diets for pigs, particularly in the post-weaning period where the newly weaned pig is subject to considerable challenges in its new environment. This chapter briefly reviews the microbiota of the gastrointestinal tract of the young pig and the important role it plays in the early stages of life. The chapter then defines probiotics, prebiotics and synbiotics, in addition to reviewing the research conducted on the topic, including a case study where a probiotic product (Peribios™) has been used commercially to modulate the production around parturition. Finally, it looks ahead for possible future trends and offers suggestions on where to look for more information on the topic.