An ideal model for quantum well solar cells is developed and is used to theoretically explore the dependence of terminal characteristics on the host cell and quantum well properties. The model, which explicitly treats carrier generation and recombination in the quantum wells, is described and compared with an analogous ideal model for bulk homojunction cells. Open-circuit voltages, short-circuit current densities, and conversion efficiencies are then calculated as functions of the well and barrier band gaps for ideal cells in the radiative limit, assuming air-mass-zero (AM0) solar illumination at a cell temperature of 300 K. Qualitative trends in these characteristics and regimes of operation are identified, the effects of non-radiative recombination are explored, and idealized approximations used in the model are assessed. Finally, published experimental data for quantum well solar cells are surveyed and discussed, and are found to exhibit strong qualitative consistencies with predictions from the ideal analysis. Results from this work provide the most comprehensive qualitative picture of quantum well solar cell operation yet proposed, and should serve as a useful guide for designing and interpreting the performance characteristics of quantum well cells fabricated from a wide variety of materials.