The Alzette (Uelzecht in Luxembourgish) flows through France and Luxembourg. It originates in the French town of Thil, in the department of Meurthe-et-Moselle (Grand Est region). It flows through the French towns of Villerupt and Audun-le-Tiche, before crossing the border into Luxembourg and the town of Esch-sur-Alzette. It weaves through a vast alluvial plain of marly terrain, then flows into a narrow valley around Hesperange, carving the sandstone into gorges, before reaching Luxembourg City and flowing on to Mersch.
The Alzette joins the Sauer on the outskirts of Ettelbruck.
With a total course of 73 km, the Alzette is one of the longest rivers in Luxembourg, together with the Sauer. The Alzette is characterised by a highly variable hydrological regime upstream of its catchment area due to the impermeable marly terrain. This regularly causes flooding in the towns it traverses.