The standard polarization formalism considers beam-like light (with a clear main direction of propagation), for which the transversality of the electromagnetic field implies that only two Cartesian components of the electric field vector are significant. However, when light is strongly focused and/or contains evanescent waves, all three electric field vector components can be significant. This talk discusses the extension into this regime of standard polarization concepts such as the degree of polarization, the Stokes parameters, and the Poincaré sphere. It is shown that the presented formalism for 3D polarization is particularly useful for applications in single molecule orientation and localization microscopy (SMOLM), where it serves in the design and analysis of novel microscopy techniques.