Feeding intolerance is a well-known phenomenon in the NICU and is linked to morbidity and mortality in the premature infant. However, a universal definition for this concept is lacking. Properly defining a concept is a key step in a successful research project. A concept analysis is an examination of the fundamental elements of a concept to bring clarification and definition to the topic of interest. The purpose of this concept analysis was to clarify the phenomenon of feeding intolerance in the premature infant and to provide a universal conceptual and operational definition for researchers and clinicians to use in practice theory.