In this paper we present a unified approach for determining the reflectance and transmittance properties of single-layer and multilayer optical and quantum thin-film structures using a unified set of equations based on the similarity of classical Maxwell and newly formulated relativistic Dirac vector field equations. A review of these field equations and the corresponding wave equations is presented. Electromagnetic plane-wave and quantum mechanical matter-wave solutions that satisfy these equations and their properties are reviewed. Single-layer optical and quantum thin film analyses lead to a unified set of analytical equations that predict their reflectance and transmittance characteristics. A unified theory conversion table describes how to convert classical electrodynamic quantities into relativistic quantum mechanical quantities to use a set of unified equations. The unified approach was extended to multilayer optical and quantum mechanical thin-film structures. Numerical results are presented for single-layer and multilayer optical and quantum thin film architectures. MATLAB software was employed for computations and graphics.