Lier is an affluent municipality in Buskerud county, Norway. The administrative centre of the municipality is the village of Lier. The municipality of Lier was established on 1 January 1838 (see formannskapsdistrikt). The area Åssiden was transferred from Lier to the neighboring municipality of Drammen on 1 July 1951.
The coat-of-arms is from modern times and was designed by Hallvard Trætteberg. They were granted on 14 August 1970. The arms show five silver-colored apple blossoms on a red background. They area is well-known for the production of various types of fruit, berries, vegetables, and flowers, so this was chosen as a symbol of the area's lush scenery and agriculture.