  This article provides an introduction to event-triggered coordination for
multi-agent average consensus. We provide a comprehensive account of the
motivations behind the use of event-triggered strategies for consensus, the
methods for algorithm synthesis, the technical challenges involved in
establishing desirable properties of the resulting implementations, and their
applications in distributed control. We pay special attention to the
assumptions on the capabilities of the network agents and the resulting
features of the algorithm execution, including the interconnection topology,
the evaluation of triggers, and the role of imperfect information.
  The issues raised in our discussion transcend the specific consensus problem
and are indeed characteristic of cooperative algorithms for networked systems
that solve other coordination tasks. As our discussion progresses, we make
these connections clear, highlighting general challenges and tools to address
them widespread in the event-triggered control of networked systems.
