In the first half I will start with an informal introduction to Gromov-Witten invariants. In a joint work with Y.P. Lee and motivated by the crepant transformation conjecture for ordinary flops, we discovered that Gromov-Witten invariants of a projective bundle are uniquely determined by those of the base and the Chern classes under certain conditions. I will state this as well as a preceeding result. In the second half, I will sketch our approaches, and discuss some observations along with further ideas. Speaker(s): Honglu Fan (Utah)