If you come from afar, the airfligt is most likely your only option

Use Momondo to find the flight that suits you best. We recommend that you buy a CO₂ quota as compensation for the flight on www.climatecare.org. Find your flight:

From the airport you can either take the metro to Nørreport Station and switch to regional trains bound for Kalundborg, Nykøbing Falster, Ringsted, Holbæk or Borup. These trains stop at Roskilde Station on the way. You can also take a train from the airport to Copenhagen Central Station and from there take a train to Roskilde Station. Please notice, intercity trains may charge an extra fee for regional travels between Copenhagen and Roskilde.

Find your journey from the airport to Roskilde Festival with The Journey Planner: