  This review demonstrates the unique role of the neutrino by discussing in
detail the physics of and with neutrinos. We deal with neutrino sources,
neutrino oscillations, absolute masses, interactions, the possible existence of
sterile neutrinos, and theoretical implications. In addition, synergies of
neutrino physics with other research fields are found, and requirements to
continue successful neutrino physics in the future, in terms of technological
developments and adequate infrastructures, are stressed.
