Karl Anselm, 4th Prince of Thurn and Taxis, full German name: Karl Anselm Fürst von Thurn und Taxis was the fourth Prince of Thurn and Taxis, Postmaster General of the Imperial Reichspost, and Head of the Princely House of Thurn and Taxis from 17 March 1773 until his death on 13 November 1805. Karl Anselm served as Prinzipalkommissar at the Perpetual Imperial Diet in Regensburg for Joseph II, Holy Roman Emperor and Francis II, Holy Roman Emperor from 1773 to 1797.

The Princely House of Thurn and Taxis is a family of German nobility that is part of the Briefadel. It was a key player in the postal services in Europe during the 16th century, until the end of the Holy Roman Empire in 1806, and became well known as the owner of breweries and commissioner of several castles. The family has resided in Regensburg since 1748 with their seat at St. Emmeram Castle from 1803. The family is one of the wealthiest in Germany, and the current head of the House is Albert, 12th Prince of Thurn and Taxis.