From the airport:
- CERN offers a free shuttle from Geneva airport to CERN - the timetable can be found here
- If your plane arrives outside of these hours you can use the Y bus to come to CERN, timetable is here
From Geneva centre:
If you are staying at a hotel in Geneva you can catch the number 18 tram from the centre of town directly up to CERN (20 min journey from the main train station) - the timetable can be found here.
Link to Geneva public transport website