The cross-section morphologies of polymeric membranes obtained by scanning electron microscopy are presented. Membranes are prepared by a wet phase inversion process from cellulose acetate, polysulfone, polyester and a polyether type of elastomeric polyurethanes, poly(methylmethacrylate), and polyamide-nylon 4,6. Morphologies are qualitatively correlated with the turbidity appearance and its intensity during the (proto)membrane formation process and with their permeability to pure water. From the morphological characteristics, such as different cellular or dense structures, macrovoids, and polymer beads, and from the turbidity phenomena during the (proto)membrane formation, the nucleation and growth of polymer-lean or polymer-rich phase and the spinodal modes of polymer-solvent-nonsolvent ternary system decomposition are postulated.