Qassam is an acronym for the Arabic Quwat al-islamiya al-mujahida (Islamic combatant force), meaning the armed branch of an Islamic movement. It may refer to:
- Izz ad-Din al-Qassam, an influential Islamist preacher
- Izz ad-Din al-Qassam Brigades, the military wing of Hamas
- Qassam rocket, a type of rocket used by the military wing of Hamas against Israel
- Any rocket used in Palestinian rocket attacks on Israel