Nanostructured ceramic thin films and membranes are used for protective or functional purposes and prepared on dense or porous substrate materials. Wet chemical methods enable cheap, low-temperature, mass-scale manufacturing routes. They produce fine-grained porous and dense micro-structures that cannot be realized otherwise. In wet-chemical processing, clean nanoparticle dispersions are deposited on the substrate at, primarily, ambient conditions. The deposition is followed by a (rapid) thermal processing treatment to remove liquids and organic additives, to convert precursors to the target composition, and to establish the final porous and dense micro-structure. In the synthesis of precursor dispersions it is very important to obtain nanoparticles with a near-isometric shape and a fairly narrow particle size distribution, without the formation of secondary (agglomerate) structures. In particular the latter requires careful control of solution and interfacial chemistry to achieve proper colloidal stability, during and after the synthesis process. Characterization of coating integrity, defect morphology and defect population is done by decoration methods, microscopy, ellipsometry and statistical methods that employ membrane transport properties.