Mars landing vehicle descent propulsion is discussed in the light of the constraints of the mission, the environment, and the interfacing functions. The presence of a largely undefined, tenuous atmosphere is shown to produce a great variability of initial and boundary conditions for the propulsion phase of descent. The mission provides numerous subtle constraints of formidable importance to the propulsion implementation. The current requirement for prelaunch, in-situ, thermal sterilization is paramount among these. A significant, and unresolved, mission-related problem is that of the interaction of landing propulsion on the native environment. For a mission which has as its primary objective the investigation of the Mars environment, landing site alteration is a significant concern. The principal intersystem constraint is that of the flight path guidance logic choice. Several options and their propulsion implications are discussed to show the tradeoffs of guidance sophistication and thrust/impulse variability. In this paper, typical Mars propulsive lander mission objectives and constraints are tabulated, the impact of these and other interfaces are reflected in design requirements, and the criteria of design are delineated. A conceptual monopropellant mechanization is presented which satisfies most of these constraints.