Lejre is a town and municipality (Danish, kommune) on the island of Zealand in east Denmark. It belongs to Region Sjælland. The town's Old Norse name was Hleiðra. The municipality has an area of 240 km² and a total population of ca. 26,603 (2008). Its mayor is Flemming Jensen, representing the liberal Venstre political party. The municipal seat is Kirke Hvalsø.
Lejre was the capital of an Iron Age kingdom, the Lejre Kingdom, which was, according to legend, ruled by kings of the Skjöldung dynasty; it is assumed to be the predecessor of medieval Denmark. Lejre is assumed to have been the location of Heorot, the royal hall mentioned in Beowulf and other myths that are set around the year 500. Archeological remains of large halls from this period have been found. The legends of the kings of Lejre were written down in the 12th century Chronicon Lethrense.
The municipality is home to the Lejre Experimental Centre, a center for experimental archaeology and education, which includes reconstructions and recreations from different periods of Denmark’s history— from pre-history to the time of the Vikings. The centerpiece of the facility is an Iron Age village reconstruction, complete with sacrificial bog. The center is open to the public.