Lajen (; ; or ) is a comune (municipality) in South Tyrol in northern Italy, located about northeast of the city of Bolzano.
As of 30 November 2010, it had a population of 2,610 and an area of .
Lajen borders the following municipalities: Barbian, Kastelruth, Klausen, Urtijëi, Villanders, Villnöàand Waidbruck.
The municipality of Lajen contains the frazioni (subdivisions, mainly villages and hamlets) Albions, Freins (Fraina), Ried (Novale), St. Peter (San Pietro), Tanirz (Tanurza) and Tschöfas (Ceves).
According to the 2024 census, 86.26% of the population speak German, 7.14% Italian and 6.59% Ladin as first language.