In order to be admitted as doctoral students, the applicants are required to have successfully finished their scientific studies in a field that is usually related to the subject of their doctoral thesis. The curriculum must cover at least 8 semesters at a university or a comparable institution of higher education (see §7 of the Doctoral Studies Regulations).
Doctoral students may officially enroll in the University, however, enrollment is neither necessary at the time of application for the admission as a doctoral student, nor for carrying out the doctoral studies. The requirements for enrolling as a doctoral student are explained in detail here.
»If you are looking for a Doctorate at the Johannes Gutenberg University in Mainz, please apply online for admission as a doctoral student.