Trigger may mean:

• Trigger (firearms), a mechanism that actuates the firing of firearms
• Trigger pad, a device used in electronic percussion
• USS Trigger (SS-237), a submarine
• USS Trigger (SS-564), a submarine
• Trigger (horse), owned by cowboy star Roy Rogers.
• Trigger (guitar), the Martin N-20 guitar played by Willie Nelson.
• Trigger (Only Fools and Horses), a fictional character from the BBC sit-com Only Fools and Horses

In psychology and ethology:

• An event which starts other events, or incites a response. See also releaser.

In computing:

• Trigger function in event-driven programming
• Database trigger, procedural code that is automatically executed in response to certain events on a particular table in a database
• Trigger circuit, IBM's name for a flip-flop.

In physics:

• Trigger (particle physics), hardware or software based device for the (online-)selection of specific event classes from large datasets (see also: ATLAS trigger system)

In music:

• Trigger (EP), an EP by the Swedish band In Flames
• "Trigger", a bonus song by The Rasmus from their 2005 album Hide from the Sun