Senjanovic's principal research interest was and is in neutrino physics. He is one of the fathers of the Left-Right symmetric theory that led to neutrino mass long before experiment; he is best recognised for the seesaw mechanism. His other major interests are baryon and lepton number violation, dark matter, grand unification and supersymmetry, in short the physics beyond the Standard Model. In recent years he is dedicating most of his time to a possible deep connection between cosmology, low energy processes such as neutrinoless double beta decay and the high energies ones at LHC, which offer a way of probing the nature and the origin of neutrino mass.