The topic for 2018 Tianyuan Advanced Seminar on Harmonic analysis, Geometry and Partial differential equations is related to harmonic analysis and its applications. Harmonic analysis has always played an important role in mathematics. In recent years, there have been many important breakthroughs related to the Kakeya conjecture, restriction conjecture, Bocher-Riesz conjecture, local smoothing conjecture. The applications of harmonic analysis to geometry and partial differential equations has also led to new results, especially in the theory of eigenfunctions on manifolds and the long time behavior of the linear and nonlinear dispersive equations. The primary goal of the seminar is to provide an occasion for experts on these fields to communicate with each other, anticipate the trends of further projects, and help young researchers and students to be familiar with these subjects. The seminar contains a few mini-courses and a series of talks.