Polarization-sensitive optical systems include those requiring very accurate irradiance measurements and those where polarization is the intended measurement. Low-polarization optical system design is the process of minimizing system polarization introduced by surface geometry, thin film coatings and birefringent elements, and measuring system components to verify polarization performance. The complicated, multi-step, iterative low polarization optical system design process requires initial system design, witness sample fabrication and measurement, reverse engineering of fabricated coatings and coating redesign, end-to-end system polarization aberration analysis, and system measurement and calibration. Most of this process will be spent iterating between design and measurement phases until a final design is reached that can be fabricated and calibrated to perform within the desired system tolerances. This work discusses low polarization optical system design using a three-mirror off-axis camera as an example.