Q.E.D. (Japanese: Q.E.D. 証明終了, Hepburn: Kyūīdī Shōmei Shūryō) is a Japanese manga series written and illustrated by Motohiro Katou. It was serialized in Kodansha's shōnen manga magazines Magazine Great (rebranded Magazine E-no in 2009) and Monthly Shōnen Magazine+ from July 1997 to February 2014, with its chapters collected in 50 tankōbon volumes. The series follow Sou Touma, a university graduate who encounters a variety of investigative cases after returning to Japan from the US. He works with his friend, Kana Mizuhara, combining his deductive skills with Mizuhara's social gifts.

A ten-episode television drama adaptation was broadcast on NHK from January to March 2009. A manga sequel, Q.E.D. iff, started in Shōnen Magazine R in January 2015 and was transferred to Getsu Maga Kichi online manga platform in February 2023.

In 2009, Q.E.D. won the 33rd Kodansha Manga Award in the shōnen category.