A number the Marketplace provides when you qualify for a health insurance exemption. When you fill out an exemption application, the Marketplace will review it and determine if you qualify. The Marketplace will mail you a notice of the exemption eligibility result. If you qualify for an exemption, the notice will include your unique identifier, called the exemption certificate number (ECN). Each member of your household who qualifies for the exemption will get their own ECN. You’ll need your ECN when you file your federal taxes for the year you don’t have coverage.