The Affordable Care Act calls for the creation of health insurance exchanges in each state, where individuals and small employers can purchase health insurance. States have considerable flexibility in how they design and implement their health insurance exchanges. This study analyzes several exchange design options using the Urban Institute's Health Insurance Policy Simulation Model (HIPSM), looking specifically at the cost and coverage implications of creating separate versus merged small group and non-group markets; eliminating age rating in these markets; removing the small employer credit; and defining the size threshold for the small group market at 50 versus 100 workers.