Block copolymers have a rich and well-defined morphology in the melt, guided by the interaction between different blocks. When applied to membranes, block copolymers offer the possibility of precisely tuning them at the nanoscale level and combining materials with different properties in one single membrane. Ideally, by choosing the right segments and the proper membrane fabrication process, block copolymers could add advantages for various applications. Here, the state of the art and perspectives in the field of block copolymer membranes will be summarized and critically discussed. They have been used for dense membrane targeting applications in gas and liquid separations, but the most rapidly developing field is the preparation of membranes by self-assembly combined with solvent-induced phase separation. The principles and most relevant factors influencing the morphology of these membranes are described, and the advantages, drawbacks, and perspectives are discussed, also in face of the manufacture sustainability.