The Kassel–Warburg Railway is a line that connects Kassel in the north of the German state of Hesse with Warburg in eastern Westphalia.

It forms part of the Mid-Germany Railway (German: Mitte-Deutschland-Verbindung), an east–west through line in central Germany, used by long-distance and regional passenger and freight trains.

The track was originally built by the Frederick William Northern Railway (Friedrich-Wilhelms-Nordbahn-Gesellschaft, FWNG) as the Carl Railway (or Charles Railway, German: Carl Bahn) from Kassel, the capital of the Electorate of Hesse (Kurhessen), to the port of Bad Karlshafen (then called Carlshaven, German for "Port Charles", after Charles I, Hesse’s ruler from 1670 to 1730) on the left bank of the Weser, one of the northernmost places in the contiguous part of Kurhessen.

Soon after the completion of the line, rail transport became important for connecting with sea transport, so the Frederick William Northern Railway started building a new line from Hofgeismar-Hümme station towards Warburg in Westphalia, under an agreement between Kurhessen and Prussia.

Since the track in Westphalia was originally the responsibility of the Cologne-Minden-Thuringian Connecting Railway Company (Köln-Minden-Thüringische-Verbindungs-Eisenbahn-Gesellschaft), which in the meantime became bankrupt, it was not until 6 February 1851, that the Royal Westphalian Railway Company (Königlich-Westfälische Eisenbahn-Gesellschaft) completed the section of its Hamm–Warburg line between Warburg and the border.