Exterior and interior are two guiding principles for distinguishing the external and internal aspects of disease, the depth of the disease tendency, and the severity of the condition. In terms of external and internal, the skin, hair, and meridians of the human body are considered external and belong to the exterior, while the internal organs are considered internal and belong to the interior. For example, in external contraction warm febrile disease, when the pathogen is in the defense aspect, it belongs to the exterior, with a shallower and milder disease tendency; if it penetrates deeply into the qi aspect or the nutrient and blood aspects, it belongs to the interior, with a more severe and deeper disease tendency. Distinguishing between exterior pattern and interior pattern not only requires division based on the location of the pathological changes but, more importantly, differentiation based on the characteristics of symptoms and signs, such as cold and heat, visceral symptoms, tongue coating, and pulse condition. Exterior and interior are relative concepts and are interconnected; under certain conditions, they can transform into each other and may coexist with cold, heat, deficiency, and excess in complex presentations.