Continuous progress in observation and theory allows to study Galactic sources of Cosmic Rays in ever increasing numbers, variety and phenomenological complexity. We are presently witnessing the transition from thorough single source studies to investigations of population aspects, as well as Galactic source physics reaching out into the extragalactic domain. Some source classes do not permit such generalization owing to their uniqueness (Galactic Center), or their apparently complex class composition (gamma-ray binaries). I will review properties and phenomenology of Galactic sources in the interplay between observations and assumptions regarding their primary and secondary particles, with the focus on key results from contemporary gamma-ray astrophysics.