You can submit the thesis in the form of a self-contained book (monograph) or collection of several essays (cumulative thesis), whereby the programmes prescribe the form in part.
A cumulative thesis consists of at least three essays which comply with a standard of quality customary in renowned international journals. At least one essay must have been contributed by the Ph.D. student him or herself and must comprise a substantial part of the thesis as a whole.
The essay can be written in cooperation with other authors (co-authorship). In terms of its contribution to science, a cumulative thesis in its entirety shall satisfy the same academic requirements as a thesis in the form of a monograph. Depending on the Ph.D. programme, there are different specifications for the cumulative thesis. Any submission of constituent parts that had been published before the student took up his/her Ph.D. studies shall not be admissible.