The invention relates to a process for making porous cross-linked cellulose membranes and processes for coupling a chromatography ligand to cross-linked cellulose membranes. The invention provides methods for separating a first component from a second component in a solution based upon a difference in the size of the first and second components, and methods for separating target molecules from other components in a solution comprising use of membranes obtainable by the process of the invention. The method has particular utility in separating proteins from cell lysates and cultures.