Book excerpt: This monograph provides a comprehensive overview on a class of nonlinear dispersive equations, such as nonlinear Schr dinger equation, nonlinear Klein Gordon equation, KdV equation as well as the Navier Stokes equations and the Boltzmann equation. The global wellposedness to the Cauchy problem for those equations are systematically studied by using the Harmonic analysis methods. This book is self-contained and may also be used as an advanced textbook by graduate students in analysis and PDE subjects- and even ambitious undergraduate students.