Purpose of Review: This literature review summarizes the evidence for and against the impact of prebiotics on brain function and behavior in older adults.Recent Findings: Current evidence generally supports the intake of prebiotics to increase beneficial gut bacteria concentrations. These bacteria appear to impact endocrine, immunologic, and neuronal communication along the gut-brain axis to alter brain function and behavior.Summary: Preliminary evidence in human studies consistently support prebiotics doses of ~ 5–10 g/d as safe to improve brain function (i.e., learning and working memory) and behavior (i.e., anxiety and mood). However, these studies are mainly of short duration (4–12 weeks) and limited to healthy, young, and middle-aged adults. More research is needed to identify a safe and effective dose, duration, and delivery method, particularly among diseased, older adults.