The chapter discusses various facets of thin films and its composition with relation to microstructure and how such factors determine its features and characteristics. Thin films which are used in applications such as solar cells, medicinal implants, and protective and semiconductor devices have distinct characteristics due to the inherent structural features as well as since they are nanoscale in thickness. There are characteristics such as mechanical strength, electrical and thermal conductivity, optical transparency, and chemical stability among others which play a very large role in their usage and these are dictated by the composition of the material. The former techniques like XPS, EDS, XRD, and SEM/TEM behave well in the determination of the composition of the material but the techniques such as XRD, SEM, TEM, and AFM are used for the analysis of microstructure of the particular material. This chapter explores several ways in which compositional changes can increase many desirable and favorable properties, such as increasing the optical transmission/absorption by modifying the material’s composition; strengthening the tensile strength through alloying; modifying the material’s electrical conductivity by doping. By comprehending, modifying, and synchronizing such variables, thin films can be optimized for specific applications and pave the innovations in electronics, optoelectronics, energy storage, and much more and thereby bridging the scientific advancement of material science and technology.