Thin Solid films are usually thermodynamically unstable in the as-deposited state. Heating can lead to fragmentation of a thin film and the formation of micro-/nano- solid particles, which is well-known as solid-state dewetting in materials science. This process is often driven by the minimization of the total interfacial energy of the system. In this talk, I will talk about how to theoretically explore this fascinating phenomenon. Taking the 2D case for example, I will explain the main idea behind these approaches, which includes how to derive mathematical models and how to use parametric finite element methods to numerically solve these models. Some extensions to the 3D case will be also presented.