The authors developed the concept differentiate as applied to the advanced practice nurse (APN) due to the lack of a current theory regarding the subject in the existing nursing literature. For instance, the APN uses differential diagnosis daily in practice. A concept analysis of differentiate according to the Walker and Avant methodology and applied to the APN can assist the APN to conduct a differential diagnosis accurately to create a safer environment for the patient. Attributes of the concept differentiate, include the following: (a) critical thinking, (b) evidence-based literature, (c) Distinguish, (d) differences, (e) complexity, and (f) complete. In addition to attributes of the differentiate concept, antecedents and consequences further elucidate the concept differentiate, and a model representation combines these three aspects to create a complete picture of the concept differentiate applied to the APN. A model, borderline, and contrary case provide real-life APN examples of the concept. Finally, the authors explore the method for conducting a proper differential diagnosis in the APN's practice to begin the patient's healing process.