Health Maintenance Organization (HMO) plans, Preferred Provider Organization (PPO) plans, and High Deductible Health Plans (HDHP) with a Health Savings Account (HSA) are the most frequent types of employer health insurance plans. HMO plans typically require employees to use a network of doctors and specialists, and specialist care usually requires a referral. PPO plans allow greater choice in healthcare providers but sometimes have higher rates. HDHPs with HSAs feature lower premiums but larger deductibles, allowing employees to save tax-free in an HSA for medical expenses.