The demand for cost-efficient separations requires membranes with high gas flux and high selectivity which opens the path for further improvements. Mixed matrix membranes (MMMs) made from 33.3 wt % ZIF-8 in 6FDA-durene were tested at 35 degrees C and 3.5 atm. At 33.3 wt % loading of ZIF-8, H-2, N-2, O-2, and CH4 gas permeabilities increased approximately 400%. Cross-linking the surface of this MMM, by reacting with ethylenediamine vapor, yielded a 10-fold increase in H-2/CO2, H-2/N-2, and H-2/CH4 selectivities with respect to 6FDA-durene, preserving 55% of the H-2 permeability of 6FDA-durene. The permselective properties of the cross-linked skin of the MMM fall above the most recent permeability selectivity trade-off lines (2008 Robeson upper bounds) for H-2/CO2, H-2/N-2, and H-2/CH4 separations. To the best of our knowledge, this is the first example of a cross-linked ZIF/polymer MMM for gas separation.