Often, rhinoplasty patients present not just for aesthetic correction, but for improvement of their nasal breathing due to functional abnormalities or problems. Because the aesthetic and functional problems must be addressed together, an understanding of both the internal and external anatomy is essential. In this article, the authors review the differential diagnosis of nasal obstruction and the important components of a thorough examination. In this article, medical treatment options are not discussed, but just as an exacting aesthetic analysis leads to an appropriate cosmetic rhinoplasty plan, a thorough functional analysis will dictate the appropriate medical or surgical treatment.