Usage of major explantory models in karst geomorphology is traced. Their inadequacy by reason of the dominance of single variables is demonstrated and a simplified multi-variable systems model is proposed as an alternative. Since both individual karst land forms and the totality of each distinctive karst assemblage is a function of the solution process acting on the karst host rock, development is controlled by the interaction of variables. No single control operates although one may dominate. A systems model for karst development is proposed as a better framework for explanation. To demonstrate its applicability it is used to explain differences in karst assemblages from southern Africa. The karst areas are hosted by a wide variety of limestones that can be broadly divided into resistant crystalline sparities and softer, porous micrites.