We consider a coupled Patlak-Keller-Segel-Navier-Stokes system in R^2 that describes the collective motion of cells and fluid flow, where the cells are attracted by a chemical substance and transported by ambient fluid velocity, and the fluid flow is forced by the friction induced by the cells. The main result of the paper is to show the global existence of free-energy solutions to the 2D Patlak-Keller-Segel-Navier-Stokes system with critical and subcritical mass. This is joint work with Juncheng Wei and Yifu Zhou. Speaker(s): Chen-Chih Lai (UBC)