Nearly 12.7 million individuals signed up for coverage in the Affordable Care Act's (ACA) health insurance marketplaces during the third open enrollment period, and by the end of March there were 11.1 million consumers with active coverage. States that operate their own marketplaces posted a year-to-year enrollment gain of 8.8 percent. To maintain membership and attract new consumers, the statebased marketplaces must sponsor enrollment assistance programs and conduct consumer outreach. These marketplaces relied heavily on such efforts during the third enrollment period, despite declining funding. Goal: To learn which outreach strategies, assistance programs, and other factors marketplace officials viewed as having exerted the greatest influence on enrollment. Methods: Survey of officialsrepresenting each of the 17 state-based marketplaces (15 responses). Key findings andconclusions: The cost of coverage and low health insurance literacy pose significantbarriers to enrollment for many consumers. Marketplaces sought to overcome themby encouraging consumers to obtain in-person enrollment assistance from ACAcreatedassistance programs and from insurance brokers, and by partnering with community organizations for outreach activities. Many marketplaces also enhanced their web portals to make them easier to navigate and to give consumers better tools with which to evaluate their coverage options.