In this talk I will explain some recent developments in Gromov-Witten theory (joint with Y. Ruan), which are closely related to several areas of mathematics and physics such as the
surgery problem of Gromov-Witten invariants, birational geometry, mirror symmetry of Calabi-Yau orbifolds, McKay correspondence, as well as
Landau-Ginzburg models and M(atrix) theory in physics.