Joseph Hansen (26 April 1863 – 29 June 1943) was an influential German historian of witchcraft persecutions, and an archivist in the city of Cologne, where at the age of 80 he was killed, along with his wife, by the bombs of World War II.

Joseph Leonhard Hansen was born in 1863 in Aachen and studied at the Universities of Bonn, Berlin, and Münster, earning a doctorate in 1883. From 1891 until his retirement in 1927, he was director of the Historical Archive of the City of Cologne. From 1893 to 1927 he was also chairman of the Society for Rhenish History.

Hansen has been referred to as liberal and "freethinking." Hansen was raised Catholic in Aachen and resided in historically Catholic Cologne, with its famous Cologne Cathedral, nonetheless some have referred to him as "anti-clerical."

In 1900, Hansen published Zauberwahn, Inquisition und Hexenprozess im Mittelalter und die Entstehung der grossen Hexenverfolgung (Magical Illusion, Inquisition, and Witch Trials in the Middle Ages, and the Formation of the Larger Persecution of Witches) and the following year a companion volume of background materials was published (Quellen = Sources), Quellen und Untersuchungen zur Geschichte des Hexenwahns und der Hexenverfolgung im Mittelalter: Mit einer Untersuchung der Geschichte des Wortes Hexe (1901).

In 1905, Hansen published a German translation of Henry Charles Lea's three-volume History of the Inquisition in the Middle Ages.

In 1921, Hansen was elected a corresponding member of the Göttingen Academy of Sciences. In 1925, he was accepted as a corresponding member of the Prussian Academy of Sciences.

In 1943, age 80 Hansen and his wife Johanna (1872–1943) were killed in a bombing raid on Cologne.

Wolfgang Behringer writes that Hansen "unquestionably delivered the consummate synthesis of previous witchcraft studies."