Control of the thin-film thickness is very crucial which is described in the chapter, “Film Thickness and Its Influence.” In most of the applications, there is a need for a thin film that requires the thin film to be fabricated with great accuracy of thickness. This chapter focuses on some of the enhanced approaches of measuring thickness that include ellipsometry, profilometry, and atomic force microscopy before concluding. Further, the role of film thickness on other characteristics like optical activities, electrical conductance, and mechanical solidity is also described, which again illustrates how films can be designed for application use. Field of applications ranging from microelectronics and optical coatings to biomedical devices as well as sensors, precise management and measurement of film thickness is necessary for effectiveness and development in these fields. Altogether, it is endorsing the theme of this chapter that film thickness assumes a significant position in studying thin films and applying them to various technologies.