Gummy smile constitutes a relatively frequent aesthetic alteration characterized by excessive exhibition of the gums during smiling movements of the upper lip. It is the result of an inadequate relation between the lower edge of the upper lip, the positioning of the anterosuperior teeth, the location of the upper jaw, and the gingival margin position with respect to the dental crown. Altered Passive Eruption (APE) is a clinical situation produced by excessive gum overlapping over the enamel limits, resulting in a short clinical crown appearance, that gives the sensation of hidden teeth. The term itself suggests the causal mechanism, i.e., failure in the passive phase of dental eruption, though there is no scientific evidence to support this. While there are some authors who consider APE to be a risk situation for periodontal health, its clearest clinical implication refers to oral esthetics. APE is a factor that frequently contributes to the presence of a gummy or gingival smile, and it can easily be corrected by periodontal surgery. Nevertheless, it is essential to establish a correct differential diagnosis and good treatment plan. A literature review is presented of the dental eruption process, etiological hypotheses of APE, its morphologic classification, and its clinical relevance.