Villars-sous-Yens is a municipality in the Swiss canton of Vaud, located in the district of Morges.
Villars-sous-Yens has an area, , of . Of this area, or 76.6% is used for agricultural purposes, while or 16.4% is forested. Of the rest of the land, or 6.6% is settled (buildings or roads).
Of the built up area, housing and buildings made up 2.6% and transportation infrastructure made up 3.0%. Out of the forested land, 13.5% of the total land area is heavily forested and 3.0% is covered with orchards or small clusters of trees. Of the agricultural land, 59.2% is used for growing crops and 5.9% is pastures, while 11.5% is used for orchards or vine crops.
The municipality was part of the Morges District until it was dissolved on 31 August 2006, and Villars-sous-Yens became part of the new district of Morges.
The blazon of the municipal coat of arms is Vert, a letter V Argent.
Villars-sous-Yens has a population () of . , 10.4% of the population are resident foreign nationals. Over the last 10 years (1999–2009 ) the population has changed at a rate of 6.6%. It has changed at a rate of 1.5% due to migration and at a rate of 5.5% due to births and deaths.
Most of the population () speaks French (519 or 92.7%), with German being second most common (18 or 3.2%) and English being third (5 or 0.9%). There are 2 people who speak Italian.
Of the population in the municipality 121 or about 21.6% were born in Villars-sous-Yens and lived there in 2000. There were 254 or 45.4% who were born in the same canton, while 89 or 15.9% were born somewhere else in Switzerland, and 84 or 15.0% were born outside of Switzerland.
In there were 6 live births to Swiss citizens and 1 death of a Swiss citizen. Ignoring immigration and emigration, the population of Swiss citizens increased by 5 while the foreign population remained the same. There were 2 Swiss men and 3 Swiss women who emigrated from Switzerland. At the same time, there were 4 non-Swiss men and 6 non-Swiss women who immigrated from another country to Switzerland.