In view of CERN's location on both Swiss and French territories, you may need to apply for a multiple-entry Schengen visa. If so, please provide your full postal (institute) address and e-mail address so that we can send you a formal invitation. You may request the visa from either the Swiss or the French consulate, according to where you plan to stay. Visa applications should be made around 6-8 weeks before your planned date of travel.
If you need more information please do not hesitate to contact Jeanne Rostant