The growing basic and clinical investigations into the extraskeletal effects of vitamin D have revealed roles in the functioning of the immune system, generating interesting questions about this nutrient's connections to sepsis. This article briefly reviews the current science of the function of vitamin D in the immune system as well as the emerging clinical literature regarding its associations with respiratory infections, sepsis, and critical illness. Finally, we offer views on the potential future directions for research in the field by outlining potential relevant scenarios and outcomes.