- This article presents an overview of currently used principles, materials, and instrumentation for characterization of membranes. This includes conventional and advanced methods for examination of chemical and physical characteristics, morphology and porosity of membranes, transport characteristics for neutral solutes and electrolytes, surface properties, and propensity to fouling. The emphasis is given to modern techniques with highest resolution and sensitivity. The most important types of instruments and model systems used in membrane characterization are explained and illustrated by representative examples. Aspects specific to characterization of dense composites for pressure-driven and gas separations, porous membranes, and ion-selective membranes are discussed in detail.