Euler-Heisenberg (EH) Lagrangian encodes nonlinear, quantum corrections to the Maxwell Lagrangian. It predicts the photon-photon scattering as well as a set of nonlinear vacuum phenomena, analogous to the optical phenomena seen in nonlinear/birefringent crystals. In this talk, I will briefly mention the nonlinear aspects of the classical Maxwellian theory and discuss the quantum corrections brought by (EH) Lagrangian and the related observational prospects.