Tienen or Thienen (; ) is a city and municipality in the province of Flemish Brabant, in Flanders, Belgium. The municipality comprises the city of Tienen proper and the towns of Bost, Goetsenhoven, Hakendover, Kumtich, Oorbeek, Oplinter, Sint-Margriete-Houtem and Vissenaken. On January 1, 2006, Tienen had a total population of 31,835. The total area is which gives a population density of 444 inhabitants per km².