Optical thin film multilayer systems at oblique angles of incidence exhibit polarization effects because of the differences between the reflectances, transmittances, and phase shifts of the p and s states of polarization. It is shown that a thin film system is equivalent to a combination of two polarization elements, a dichroic linear polarizer and a retarder; thus, it offers the possibility of controlling the polarization states in different optical systems. The representation of thin film polarizers in the Jones calculus is given and three applications are introduced and discussed. Two of the applications are for conserving the polarization state in corner cube retroreflectors for high-power laser cavity at 1065 nm and in a penta-roof prism for long-range high-quality telescope. The last example is implemented for a divider-combiner element in bidirectional fringe-counting interferometry where the phase shifts and intensities for both states of polarization (p and s) are controlled.