Abstract: ?-Aminoamidine polymers and methods of preparing a-aminoamidine polymers by reacting by reacting one or more amines with one or more isocyanides and one or more aldehydes are described. Methods of preparing a-aminoamidine polymers from commercially available starting materials are also provided, wherein the starting materials are racemic or stereochemically pure. a-Aminoamidine polymers or salt forms thereof are preferably biodegradable and biocompatible and may be used in a variety of drug delivery systems and for other purposes as well such as, for example, coatings, additives, excipients, plastics, and materials, etc. Given the amino moiety of these ?-aminoamidine polymers, they are particularly suited for the delivery of polynucleotides. Complexes, micelles, liposomes or particles containing the inventive ?-aminoamidine polymers and polynucleotides can be prepared. The inventive ?-aminoamidine polymers may also be used in preparing microparticles for drug delivery.