If you write a doctoral dissertation, please inform yourself about copyright. Copyright protects you as an author. Publishers may ask you to transfer the copyright to them, but you are not obliged to do so.
The University is entitled to retain a copy of your dissertation at the Leiden University Libraries and to use it for its academic teaching and research. However, you possess the copyright to your own work, unless you have explicitly transferred it to someone else. Is your doctoral dissertation being published? Pay close attention to any transfer of copyright statements in the contract with your publisher. This also applies if you want to publish articles or chapters from your dissertation in other media.
You are not obliged to transfer the copyright to a publisher. SURF has produced a short film explaining how and why you can choose to retain copyright.
Contact the Copyright Information Office at the Leiden University Libraries if you require information and help on copyright.