The definition of a unit of structural evolution which can be applied to Precambrian as well as to younger areas is discussed, and the spatial unit "orogen" is selected as the most suitable term for such a unit. It means any zone in which orogenic movements occur. This term is broader than "geosyncline," for such movements are not limited to geosynclines. The orogens of the different parts of the earth vary greatly in dimension, form, and situation with respect to older zones. The stages of a "drama" (a term preferred to "orogenic cycle") are outlined and applied to an interpretation of the history of the African continent.