Esch-sur-Alzette (French pronunciation: [ɛʃ syʁ alzɛt], lit. 'Esch on Alzette'; Luxembourgish: Esch-Uelzecht [ˌæʒ ˈu̯əltsəɕt] ; German: Esch an der Alzette [ˈɛʃ ʔan deːɐ̯ ʔalˈzɛt] or Esch an der Alzig) is a university city in Luxembourg and the country's second-most populous commune, with a population of 37,922 inhabitants, as of 2025. It lies in the south-west of the country, on the border with France and in the valley of the Alzette, which flows through the city. The city is usually referred to as just Esch; however, the full name distinguishes it from the village and commune of Esch-sur-Sûre which lies 45 kilometres (28 miles) further north. The country's capital, Luxembourg City, is roughly 15 km (9.3 mi) to the north-east.
The town, first mentioned in the Middle Ages, remained a modest settlement for centuries until the discovery of iron ore in the 19th century transformed it into one of Luxembourg’s main industrial centres. The rapid expansion of mining and steel production attracted workers from across Europe, shaping Esch into a multicultural urban community. After the decline of the steel industry in the late 20th century, the city underwent structural change.