Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, relating to synthetic call initiation. In some implementations, a method includes receiving, by a call triggering module of a call initiating system for placing calls and conducing conversations between a bot of the call initiating system and human callee during the calls, data indicating a first event, determining, by the call triggering module and using the data indicating the first event, that the first event is a trigger event that triggers a workflow for the call initiating system that begins with initiating a phone call, selecting, based on the determined trigger event, a particular workflow, and in response to the selecting, initiating a phone call to a callee specified by the particular workflow.