You need to have a qualifying High Deductible Health Plan (this essentially means that you have to pay for all covered medical services (except preventative care) before your health insurance kicks in. So no copays or coinsurance before your deductible is met).
Can’t be enrolled in any other non-HSA qualified health insurance plan.
Can’t have your own or be eligible to use a general purpose Flexible Spending Account (FSA) - (e.g., your spouse cannot be enrolled in an FSA). Limited purpose FSAs are allowed for Dental, Vision, and Dependent Care if your HDHP doesn’t cover those services. Be sure to check with your employer in case this applies to your situation. If your spouse is not enrolled in an FSA and you are eligible for an FSA, but opt-out, then you would be eligible to open an HSA so long as you meet all the other criteria.
Can’t be claimed as a dependent in someone else’s tax return.
Can’t be enrolled in Medicare (Part A and Part B) or Medicaid.