The neutrino, the lightest and most weakly interacting fermion of the Standard Model, has revealed itself as the messenger of the most exciting news of the last decade in particle physics: there is Physics Beyond the Standard Model. All this thanks to the quantum-mechanical phenomenon of flavour oscillations which is intrinsically connected to the question of neutrino mass and which has been observed in a variety of physical situations. Neutrinos have also an important role in Astrophysics and Cosmology as well as in the study of our own planet. Indeed the possibility of doing tomography of the Earth\'s structure using a high energy cosmic neutrino beam has been extensively studied since it was first suggested more than twenty five years ago.In this talk I will first review the evidence for neutrino mass from existing experiments. I will then briefly comment what we can learn on more exotic forms of new physics and on the solar model from this data. In the second part I will review the different approaches to neutrino Earth tomography using high energy neutrinos. I will point out their limitations. Finally I will present our most recent observation that with the advent of second-generation kilometer-scale neutrino detectors, the idea of studying the internal structure of the Earth may be revived using atmospheric neutrinos.