Modal decomposition of light has been known for a long time, applied mostly to pattern recognition. With the commercialization of liquid crystal devices, digital holography as an enabling tool has become accessible to all, and with it all-digital tools for the decomposition of light has finally come of age. We review recent advances in unravelling the properties of light, from the modal structure of laser beams, to decoding the information stored in orbital angular momentum carrying fields. We show application of these tools to fibre lasers, solid-state lasers and structured light created in the laboratory by holographic laser beam shaping. We show by experimental implementation how digital holograms may be used to infer the intensity, phase, wavefront, Poynting vector, polarization and orbital angular momentum density of some unknown optical field. In particular, we outline how virtually all the previous ISO-standard beam diagnostic techniques may be readily replaced with all-digital equivalents, thus paving the way for unravelling of light in real-time. Such tools are highly relevant to the in situ analysis of laser systems, to mode division multiplexing as an emerging tool in optical communication, and for quantum information processing with entangled photons.