A process for the modification of amines and alcohols, comprising (i) providing a substrate having amino groups or alcohol groups, wherein said substrate is, e.g., a polysaccharide; (ii) providing a modifying agent which is a lactone, an ester, a polyester, a carbonate, a polycarbonate, a lactide, a glycolide, an anhydride, an acid, a thioester or a carbamate; (iii) providing a catalyst which is, e.g., a amino acid or an organic acid; and (iv) reacting the substrate with the modifying agent in the presence of the catalyst.