[role="xpack"]
[[trigger]]
== {watcher} triggers
++++
<titleabbrev>Triggers</titleabbrev>
++++

Every watch must have a `trigger` that defines when the watch execution process
should start. When you create a watch, its trigger is registered with the
appropriate _Trigger Engine_. The trigger engine is responsible for evaluating
the trigger and triggering the watch when needed.

{watcher} is designed to support different types of triggers, but only time-based
<<trigger-schedule,`schedule`>> triggers are currently available.

include::trigger/schedule.asciidoc[]