At its most basic level, fusion splicing is a mechanical process in which two optical fibers are welded together to form a joint. This welding is accomplished by heating the fiber tips until they attain a temperature at which they soften and coalesce. Mechanical forces, heat transfer, and mass transfer all interact to shape the fusion splice process. An engineering analysis of these phenomena can provide valuable insights into strategies for fabricating low-loss, high strength fusion splices.In this chapter, we will analyze the mechanical aspects of optical fiber fusion splicing beginning with heat transfer in Sect. 3.1. The relevant mechanical forces will be discussed in Sect. 3.2 and the theory of dopant diffusion will be covered in Sect. 3.3. In the concluding section, we will discuss the impact of stress and strain on optical fiber fusion splices.