  Multi-messenger astronomy has experienced an explosive development in the
past few years. While not being a particularly young field, it has recently
attracted a lot of attention by several major discoveries and unprecedented
observation campaigns covering the entity of the electromagnetic spectrum as
well as observations of cosmic rays, neutrinos, and gravitational waves. The
exploration of synergies is in full steam and requires close cooperation
between different instruments. Here I give an overview over the subject of
multi-messenger astronomy and its virtues compared to classical "single
messenger" observations, present the recent break throughs of the field, and
discuss some of its organisational and technical challenges.
