100th Regiment
- 100th Anti-Tank Regiment, Royal Artillery (The Gordon Highlanders)
- 100th Guards Fighter Aviation Regiment
- 100th Heavy Anti-Aircraft Regiment, Royal Artillery
- 100th Illinois Infantry Regiment
- 100th Independent Shipborne Fighter Aviation Regiment
- 100th Indiana Infantry Regiment
- 100th New York Infantry Regiment
- 100th Ohio Infantry Regiment
- 100th Pennsylvania Infantry Regiment
- 100th Regiment of Foot (disambiguation)