Lahnstein (German pronunciation: [ˈlaːnʃtaɪn]) is a verband-free town of Rhein-Lahn-Kreis in Rhineland-Palatinate, Germany.

It is situated at the confluence of the Lahn with the Rhine, approximately 6 kilometres (3.7 mi) south of Koblenz.

In religious affairs, it is assigned to the Roman Catholic Diocese of Limburg and to the Evangelical Church in Hesse and Nassau.

Lahneck Castle, situated high above Oberlahnstein, was built between 1240 and 1245 and served as a residence of the Archbishop-Electors of Mainz.

Other sights in Lahnstein include Martinsburg Castle on the bank of the Rhine in Oberlahnstein, the Allerheiligenbergkapelle, St. John's Abbey (Johanneskloster), and the Rheinsteig hiking trail.

[4] Around c. 369–370 AD, the Romans built a burgus (or watch tower) at the mouth of the Lahn on the site of present-day Niederlahnstein.

It served the Rhine border fortifications and acted as a sentry for the fortress at Koblenz (Latin: Castellum apud Confluentes).

It was this tower made of stone, which was called the "fortified house on the Lahn" (Latin: domus fortis supra Lonetam) in the Middle Ages, that gave the town its name.

[5] Traces of the Roman Limes Germanicus, the border fortifications built to safeguard the Empire from the Germanic tribes, still exist today about 8 km (5 mi) from the town in the Oberlahnstein city forest.

Siegfried had Lahneck Castle built in 1226 to protect these territories, which were Mainz's northernmost exclave (in religious matters, Oberlahnstein was under the Archbishopric of Trier).

On 4 June 1400, King Wenceslaus of Germany was called by the four Rhenish Prince-electors to appear before them in Oberlahnstein to answer charges of failing to maintain the public peace.

In Rhens, the following day, Rupert, Count Palatine of the Rhine, was elected the new "King of the Romans".

Between 1632 and 1646, during the Thirty Years War, both towns experienced multiple occupations by Swedish, Imperial, Hessian and French troops.

[6] This former mining village is situated about 5 km (3.1 mi) east of Lahnstein proper near the town of Frücht.

The distribution of seats in the town council (German: Stadtrat) is as follows: Lahnstein offers a variety of climbing and hiking trails The new Rhine mountain trail from Bonn to Wiesbaden in traverses the district of Lahnstein on the health resort and the Ruppertsklamm.