The clinical goals of intravenous lipid emulsions (ILEs) have changed since their initial development. In the past, 100% soybean oil was used to provide energy and prevent an essential fatty acid deficiency. Now, different oil sources are used with the goal of improving nutritional status and preventing common neonatal comorbidities. We now have a better understanding of specific ILE constituents, namely, fatty acids, vitamin E, and phytosterols, and how these components contribute to complications such as intestinal failure-associated liver disease. This review addresses the development and composition of different ILEs and summarizes how individual ILE ingredients affect infant metabolism and health.