Creatine is a major component of energy metabolism that is abundant in human skeletal muscle, brain, and heart. Either synthesized internally or provided via an omnivorous diet, creatine is required for normal growth, development, and health. Recent advances in creatine nutrition and physiology suggest that the quantity of creatine the body naturally synthesizes is not sufficient to meet human needs. As a result, humans have to obtain enough creatine from the diet, which nominates creatine as an essential nutrient in certain circumstances. In this article, we summarize arguments that creatine should be considered a conditionally essential nutrient for humans and propose several questions that should be addressed in future research.