The Free State of Bottleneck (German: Freistaat Flaschenhals) was a short-lived quasi-state that existed from 10 January 1919 until 1 July 1920. It was formed from part of the Prussian province of Hesse-Nassau as a consequence of the occupation of the Rhineland following World War I. The Bottleneck is now part of the German states of Hesse and Rhineland-Palatinate.

Following the Armistice of 1918, Allied forces occupied the German territory west of the Rhine. To maintain a military presence on the eastern side, the Allied powers extended their zones of occupation by creating three semi-circular bridgeheads of 30 km (19 mi) radius, radiating from Cologne (British zone), Koblenz (American zone), and Mainz (French zone).

The French and American zones did not meet entirely, leaving a narrow gap on the eastern side of the Rhine containing the Wisper valley, the towns of Lorch and Kaub, and villages of Lorchhausen, Sauerthal, Ransel, Wollmerschied, Welterod, Zorn, Strüth and Egenrod.

Surrounded by the two Allied bridgeheads, the Rhine to the south-west and no roads nor any railways towards the north-east, this small region was effectively cut off from the rest of Germany and subsequently separated from the administration of the Weimar Republic.

Owing to the circular nature of the Allied bridgeheads, this enclosed territory took on the shape of a bottleneck, hence the name that was given to the microstate, when it was declared on 10 January 1919.

The region contained approximately 17,000 people and its largest town, Lorch, was established as the capital. The Mayor of Lorch, Edmund Pnischeck [de], was subsequently elected president of the small territory. Pnischeck headed the Bottleneck's administration for all of its existence, which even oversaw the production of its own stamps. Also, due to the isolated economy, Pnischeck issued emergency currency, which soon gained considerable value in neighboring occupied territories.

There were no roads connecting the Bottleneck to unoccupied Germany, trains were not permitted to stop there, and air or river transportation was impossible. The movement of goods and post to and from the state was only made possible by smuggling. Pnischeck's first action was to have a temporary road built between the Rhine and Heidenrod. He also had a telegraph line constructed that bypassed Allied occupied territory, with help from the Limburg an der Lahn telegraph office.

Once, a French train loaded with coal from the Ruhr valley was hijacked from neighbouring Rüdesheim am Rhein and taken to the Bottleneck, where the coal was distributed among the populace for heating purposes. Also, nighttime ship transports were a proven means of supplying the bottleneck with essential goods, requiring 20 to 25 horse-drawn carts to unload. Limburg district administrator and local merchant, Robert Büchting [de], also supplied the Bottleneck, and was helped by a "Minister of Railways" based in Lorch, who had access to a large fleet of vehicles belonging to the "Association for the Chemical Industry in Frankfurt." According to Pnischeck, such actions were so successful that the Bottleneck may have been one of the first regions in Germany to abolish food rationing.