Josef Mašín (26 August 1896 – 30 June 1942) was an army officer of Czechoslovakia and member of the Czech underground resistance against the Nazis.

After the occupation of Czechoslovakia by Nazi Germany he, together with Josef Balabán and Václav Morávek, formed a resistance group concentrated on intelligence gathering and sabotage.

While more resistance groups existed, this one, aptly named Three Kings, is the most known among the Czech Republic.

As part of the German retaliatory measures for the assassination of Reinhard Heydrich he was shot and killed, aged 45.

His sons – then 13 and 15 years old – got Medals for "personal bravery during the war" from president Edvard Beneš.