abstract: I will discuss the analogue of Nevanlinna theory in one and several variables and the theory of Diophantine approximations, centering aroud the so-called second main theorem and abc-conjecture. I would like to present some obsevations on the classical results in these subjects from this viewpoint, and then discuss some new results motivated by the analogue which have been obtained in these several years. Lang's conjecture and Kobayashi hyperbolicity will be also discussed.