  The new field of multi-messenger astronomy aims at the study of astronomical
sources using different types of "messenger" particles: photons, neutrinos,
cosmic rays and gravitational waves. These lectures provide an introductory
overview of the observational techniques used for each type of astronomical
messenger, of different types of astronomical sources observed through
different messenger channels and of the main physical processes involved in
production of the messenger particles and their propagation through the
Universe.
