in ecology, the final stage of biotic succession attainable by a plant community in an area under the environmental conditions present at a particular time. For example, cleared forests in the eastern United States progress from fields, to old fields (with colonizing trees and shrubs), to forests of these early colonists, and finally to climax communities of longer-lived tree species. The species composition of the climax community remains the same because all the species present successfully reproduce themselves and invading species fail to gain a foothold. Because climatic changes, ecological processes, and evolutionary processes cause changes in the environment over very long periods of time, the climax stage is not completely permanent.

(Greek: “ladder”), in dramatic and nondramatic fiction, the point at which the highest level of interest and emotional response is achieved.

In rhetoric, climax is achieved by the arrangement of units of meaning (words, phrases, clauses, or sentences) in an ascending order of importance. The following passage from Melville's Moby Dick (1851) is an example:

In the structure of a play the climax, or crisis, is the decisive moment, or turning point, at which the rising action of the play is reversed to falling action. It may or may not coincide with the highest point of interest in the drama. In the influential pyramidal outline of five-act dramatic structure, advanced by the German playwright Gustav Freytag in Die Technik des Dramas (1863), the climax, in the sense of crisis, occurs close to the conclusion of the third act. By the end of the 19th century, when the traditional five-act drama was abandoned in favour of the three-act, both the crisis and the emotional climax were placed close to the end of the play.