AdS/CFT is the conjectured relationship between a conformal field theory in d-dimension and a gravity theory in (d+1)-dimension. It is the most successful realization of the holographic principle in quantum gravity and also provides a powerful toolkit for studying strongly coupled quantum field theories. In the talk, I will review the concept, dictionary and computation techniques of AdS/CFT together with some recent progress like Ryu-Takayanagi entropy formula, Sachdev-Ye-Kitaev model, and black holes.