The main difference is that there is a group of health insurers called Gesetzliche Krankenkassen (health insurers according to law), which are heavily regulated and whose service offerings are governmentally controlled. If you earn less than a specified amount of money as an employee, you are required to get coverage from such an institution. Which institution is up to you, it just has to offer you the contract according to law. There are about 100 different health insurers in Germany, which offer coverage according to law, and most of them operate through the whole of Germany. You are free to buy additional insurance if you want more or better services. If you are on social security, you are automatically insured by a Gesetzliche Krankenkasse. If you are self employed, operate your own business or earn more than the limit, you are completely free in your choice of health insurance.