Health insurance coverage is mandatory for everyone living in Germany and you are requiered to have health insurance coverage for the whole duration of your stay.
If you have a working contract
and your salary is between €520 /month or €66,600/year,
you are entitled to join the statutory health insurance. Statutory health insurance can already be arranged in advance, but will only cover you from the first day of your working contract.
If you have a fellowship
, you will need to take a private health insurance.
If you earn less then €520 /month or more then €66,600/year, you can choose between private or statutory health insurance.