Lausen is a municipality in the district of Liestal in the canton of Basel-Country in Switzerland.
Lausen is first mentioned in 1275 as in villa et banno Langenso. In 1305 it became the property of the Bishop of Basel, passing in 1400 to the city of Basel.
Lausen has an area, , of . Of this area, or 23.6% is used for agricultural purposes, while or 50.5% is forested. Of the rest of the land, or 25.0% is settled (buildings or roads), or 0.5% is either rivers or lakes and or 0.4% is unproductive land.
Of the built up area, industrial buildings made up 3.8% of the total area while housing and buildings made up 12.9% and transportation infrastructure made up 5.4%. Power and water infrastructure as well as other special developed areas made up 1.3% of the area while parks, green belts and sports fields made up 1.6%. Out of the forested land, 48.4% of the total land area is heavily forested and 2.2% is covered with orchards or small clusters of trees. Of the agricultural land, 9.5% is used for growing crops and 12.4% is pastures, while 1.6% is used for orchards or vine crops. All the water in the municipality is flowing water.
The municipality is located in the Liestal district, in the mid-Ergolz valley, south-east of Liestal.
The blazon of the municipal coat of arms is Gules, two pick-axes Or in saltire, in Chief Sable three Bezants one and two.
Lausen has a population () of . , 23.9% of the population are resident foreign nationals. Over the last 10 years (1997–2007) the population has changed at a rate of 5.7%.
Most of the population () speaks German (3,953 or 85.1%), with Italian language being second most common (272 or 5.9%) and Albanian being third (89 or 1.9%). There are 43 people who speak French and 4 people who speak Romansh.
the gender distribution of the population was 49.4% male and 50.6% female. The population was made up of 3,674 Swiss citizens (75.6% of the population), and 1,184 non-Swiss residents (24.4%) Of the population in the municipality 1,040 or about 22.4% were born in Lausen and lived there in 2000.