  The gravitational wave window onto the universe will open in roughly five
years, when Advanced LIGO and Virgo achieve the first detections of high
frequency gravitational waves, most likely coming from compact binary mergers.
Electromagnetic follow-up of these triggers, using radio, optical, and high
energy telescopes, promises exciting opportunities in multi-messenger time
domain astronomy. In the next decade, space-based observations of low frequency
gravitational waves from massive black hole mergers, and their electromagnetic
counterparts, will open up further vistas for discovery. This two-part workshop
at featured brief presentations and stimulating discussions on the challenges
and opportunities presented by gravitational wave astronomy. Highlights from
the workshop, with the emphasis on strategies for electromagnetic follow-up,
are presented in this report.
