Equilibrium-thickness, intergranular films (IGFs) have been observed in various ceramic materials. Recently, surficial amorphous films (SAFs) of similar character have also been found. Furthermore, a series of studies revealed the stabilization of disordered (quasi-liquid) IGFs and SAFs well below the bulk solidus or eutectic temperatures, wherein analogies to the phenomena of premelting and prewetting can be made. Accordingly, combined interfacial premelting and prewetting models have been developed using a diffuse-interface theory. This paper outlines the key results of two model experiments in support of the above theory: namely observation of quasi-liquid grain boundary films (metallic IGFs) in W-Ni and searching of a complete wetting transition for Bi2O3 on ZnO where SAFs become macroscopically thick. We propose that simple combined interfacial premelting and prewetting models apply to metallic IGFs, but only serve as a basis to understand IGFs and SAFs in ceramics where additional interactions, e.g. dispersion forces and space-charges, should be added separately and may result in more complex behaviors.