In this talk, we will briefly discuss Strichartz estimates which play an important role in the study of long-time behavior of dispersive equations. We will focus on the model equations, Schroedinger equations in R^n for n\geq 3. Starting from basic free Schroedinger equations, we will sketch some extensions for Schroedinger equations with potentials. To derive Strichartz estimates for Schroedinger equations with potentials, we will emphasize an imporant idea based on the smoothness of an operator in Kato's sense introduced by Rodnianski-Schlag. If time permits, we will also discuss some further extension for charge transfer models.