Health Insurance
Most Germans are members of the government health system (GKV), and for all employees it is mandatory. It is a statutory regulation. You can choose one health insurance out of about 103 health insurances in Germany.
Read more about the statutory health insurance regulations:
https://www.gkv-spitzenverband.de/english/statutory_health_insurance/statutory_health_insurance.jsp
Here you find the list of German Health insurances (in German only):