The ACA Marketplaces specifically target nonelderly adults with incomes above the national Medicaid-eligibility cutoff (138 percent of the federal poverty level) who are currently uninsured or are purchasing individual coverage. Thus, how well this population understands health insurance plans, and its willingness to tackle the challenges of plan selection, will largely determine the ACAs enrollment success. These challenges range from demonstrating income eligibility and citizenship status to comparing premium, benefit, cost-sharing, and provider network alternatives. Selection and enrollment may be particularly demanding for uninsured adults who have no previous experience with, or negative impressions of, shopping for health coverage. In this brief, we focus on the prior nongroup market experience of the currently uninsured adult Marketplace target population, to assess how their perceptions of coverage cost and affordability are likely to influence the ACAs success in reaching its enrollment targets.