Copyright © 2020 by the American Academy of Pediatrics. CONTEXT: The World Health Organization recommends tummy time for infants because of the benefits of improved motor development and reduced likelihood of plagiocephaly. Because of poor uptake of these recommendations, the association of tummy time with other health outcomes requires further investigation. OBJECTIVE: To review existing evidence regarding the association of tummy time with a broad and specific range of infant health outcomes. DATA SOURCES: Electronic databases were searched between June 2018 and April 2019. STUDY SELECTION: Peer-reviewed English-language articles were included if they investigated a population of healthy infants (0 to 12 months), using an observational or experimental study design containing an objective or subjective measure of tummy time which examined the association with a health outcome (adiposity, motor development, psychosocial health, cognitive development, fitness, cardiometabolic health, or risks/harms). DATA EXTRACTION: Two reviewers independently extracted data and assessed their quality. RESULTS: Sixteen articles representing 4237 participants from 8 countries were included. Tummy time was positively associated with gross motor and total development, a reduction in the BMI-z score, prevention of brachycephaly, and the ability to move while prone, supine, crawling, and rolling. An indeterminate association was found for social and cognitive domains, plagiocephaly, walking, standing, and sitting. No association was found for fine motor development and communication. LIMITATIONS: Most studies were observational in design and lacked the robustness of a randomized controlled trial. High selection and performance bias were also present. CONCLUSIONS: These findings guide the prioritization of interventions aimed at assisting parents meet the global and national physical activity guidelines.