In this talk, I would like to talk about mathematical treatments for synchronization and flocking phenomena. In the first part, I will introduce a simple approach to Kuramoto model to describe synchronization. I will present asymptotic formation and nonlinear stability of phase-locked states of solutions. In the second part, I will talk on a kinetic-fluid model for the interaction between flocking particles and incompressible fluid. For the proposed model, I will discuss global existence of weak and strong solutions, and long-time behaviour of solutions.