Lahnstein is a verband-free town located in the Rhein-Lahn-Kreis district of Rhineland-Palatinate, Germany. It is situated at the confluence of the Lahn and Rhine rivers, approximately 6 kilometres (3.7 mi) south of Koblenz.
The town was established in 1969 through the merger of two previously independent municipalities: Oberlahnstein, located on the south side of the Lahn, and Niederlahnstein, situated on the north side. As of 2020, the population of Lahnstein was 18,030.