An initiator can refer to:
- A person that takes an initiative in making something happen.
- Modulated neutron initiator, a neutron source used in some nuclear weapons
- Pyrotechnic initiator, a device containing a pyrotechnic composition used primarily to ignite other, more difficult to ignite materials
- Radical initiator, chemical substances that can produce radical species under mild conditions
- Photoinitiator, chemical substances that produce radical specials upon exposure to light
- SCSI initiator, the host-side endpoint of a SCSI session