Every Israeli resident must be registered to the Bituach Leumi by law, and should choose which "kupat cholim" (HMO) he wishes to be a member of. Changing a kupat cholim is possible up to twice a year.
There are 4 kupot cholim – Clalit, Maccabi, Meuhedet or Leumit. All offer the same basic service and medication basket by law, but they vary in their quality of services, variety and availability of doctors and clinics (including private doctors who have agreements with the kupat cholim), and the various upgraded plans each of them offers.