Theorists agree that the risk of folding changes as organizations age, but there is little consensus as to the general form or generative processes of age-dependent mortality. This article investigates four such processes (maturation, senescence, legitimation and obsolescence), which have been taken as competing accounts. Using two analytical levers--elaborating on the time shapes of these processes and distinguishing aging of organizations from aging of their templates (designs)--this paper differentiates these four processes and tests them jointly. Analysis of mortality rates for American communes from 1609 through 1965 strongly supports the proposed effects of maturation and senescence at the organization level and legitimation at the level of organizational templates. Results give weaker evidence that obsolescence of templates influenced mortality and that environmental drift exacerbated obsolescence. (Contains 2 tables, 3 figures, and 14 notes.)