Front Tracking is a high resolution numerical method which tracks the dynamic movement of discontinuities between two different materials or subdomains. It was first introduced by Richtmyer and Morton to solve one dimensional partial differential equations with discontinuities. It was later used for 2D high quality aerodynamic computation by Moretti, Grossman, and Marconi. Glimm et al. have used this method for the study of fluid interface instabilities since late 1980's. The FronTier code is a software library based on the front tracking method. In recent years, it has evolved into a general purpose software library for scientific computation involving dynamic motion of interfaces. I will give a general description of the method and introduce some of the physics and engineering applications using this package. In particular, I will discuss the simulation of the fluid interface instability problem by solving the PDE of gas dynamics using the front tracking code.