Book excerpt: Infant formulas are unique because they are the only source of nutrition for many infants during the first 4 to 6 months of life. They are critical to infant health since they must safely support growth and development during a period when the consequences on inadequate nutrition are most severe. Existing guidelines and regulations for evaluating the safety of conventional food ingredients (e.g., vitamins and minerals) added to infant formulas have worked well in the past; however they are not sufficient to address the diversity of potential new ingredients proposed by manufacturers to develop formulas that mimic the perceived and potential benefits of human milk. This book, prepared at the request of the Food and Drug Administration (FDA) and Health Canada, addresses the regulatory and research issues that are critical in assessing the safety of the addition of new ingredients to infants.