There is a long story of the role nonlinearity plays in optics and photonics. From the early experiments in second harmonic generation to the demonstration of optical solitons in fiber optics, the field continues to evolve in several directions. Rather than presenting well developed ideas, in this seminar I will attempt to provide examples mostly from recent experiments in need of better models. They will highlight optical phenomena for weakly and for strongly nonlinear effects. Topics I hope to cover include pulses in novel waveuides with leading fourth order dispersion, spatio-temporal dynamics in multi-mode fibers, coherent beam combining and second harmonics filaments..