By plane
Roskilde Airport IATA: RKE, ICAO: EKRK (http://www.rke.dk/RKE/UK/MAIN/) is Denmark's premier General Aviation facility with planes taking off or landing, every 5 minutes througout the day. It is also the main base for un- or semi scheduled taxi flights to the Kingdoms more remote islands; Copenhagen Airtaxi (http://www.aircat.dk) offers flights to Samsø, Læsø and Anholt for between 1,000-1,500 Kr, and more or less works as a regular airline, with flights bookable on the company website. Other options include: Samair (http://samair.dk/) to Samsø and Starling (http://www.starling.dk/ru...) to Ãrø.
By bus
Intercity buses to and from Jutland (http://www.fjernbusser.dk) lines 882 to Fjerritslev and 888 to Aarhus/Aalborg, makes stop at the Q8 gas station at Darupvej 2, by the highway. It is quite far from the city center, but there are several bus lines connecting from Roskilde Station, e.g. 600S
Important regional buses includes 600S which runs an arch around Copenhagen proper from Hillerød in the north Frederiksborg castle to Hundige Station in the south. 233 runs between Roskilde and Lejre Forsøgscenter, 234 connects with Slagelse and finaly 229E and 239 with Frederikssund.
By train
From Copenhagen Central Station København H it is about a 25 minute trip. Nearly all trains leaving Copenhagen besides those leaving for Elsinore or Sweden stops in Roskilde. Regional trains bound for Odense, Kalundborg or Nykøbing Falster are your best choices they are marked with a green "Re" sign on platform screens. There is also a small branch line with occasional trains to Køge.