What requirements must I fulfil?

Check the formal requirements
A university degree is a general prerequisite to qualify for admission to doctoral studies. Usually, a final grade point average of at least 2.5 on the German grading scale (which equals good or B+) or an examination graded "cum laude" is required.
If you earned your degree abroad, the PhD Commission of the faculty will decide on its recognition. The Commission will also check whether other proof of academic qualifications is required to meet the admission requirements for the doctoral procedure.
The exact regulations in this regard can be found in the faculties' doctoral degree regulations, see right column or scroll down.

Find an academic supervisor
If you choose to earn your doctoral degree in Göttingen and have met the prerequisites, the next step is to find a professor to be your academic supervisor. You cannot apply for admission without consent for supervision.
When seeking an academic supervisor, you should try searching on your own in your field of study. Some faculties provide lists with professors available as potential PhD supervisors. You can also contact the responsible persons at the faculty of your interest.

Clear out the financial aspects of your doctoral studies
In the natural sciences, consent from a supervisor is usually linked to funding. In the humanities and social sciences, you must organise the financing of your doctoral studies yourself. Via the links on the right, you will find a list of organisations that award scholarships as well as an overview of current jobs offered at the university.

Next step:

How to apply?