PhD candidates with employee status (werknemerpromovendi) are appointed at the Faculty of Science specifically to do PhD research. They are supervised by (a) member(s) of the Faculty staff and have an obligation to graduate. Application to a paid position occurs in response to a vacancy advertised by the University.

The initial contract is for one year. Within that period, a progress review is carried out to decide whether the contract will be extended for a maximum of three more years (full-time PhD programme).

Contract PhD candidates do not have an employment contract with Leiden University, but are funded by a scholarship, or are granted a salary and/or time by their external employer. They are supervised by (a) member(s) of the Faculty staff and have an obligation towards the grant supplier to graduate.

The PhD graduation is planned at Leiden University. PhD candidates who are applying for a personal research grant elsewhere and wish to carry out research at the Faculty of Science must first find a professor at one of the institutes who is willing to supervise them. 

External PhD candidates receive their funding from other sources than Leiden University or PhD grants. External PhD candidates are not appointed at the Faculty, but work on a PhD thesis with their own funding and in their own time. They are supervised by (a) member(s) of the Faculty but have no obligation to graduate.

The PhD graduation is planned at Leiden University. PhD candidates who wish to carry out research at the Faculty of Science first have to find a professor at one of the institutes who is willing to supervise them.