The synthesis of polymeric membranes that exhibit high permeation selectivity and high flux is a major challenge that has important technological implications. In an effort to rationally design such materials, the concept of perforated monolayers (i.e., two-dimensional arrays of porous surfactants) has been introduced. Results that have been obtained to date, using prototype systems, provide considerable incentive for exploring and exploiting such ultrathin materials as novel membranes for separation.