The results of studies of interpolyelectrolyte complexes of chitosan and different polyanions are summarised and described systematically in this book. Specific properties of chitosan as polyelectrolyte are described. The general concept of the formation of polyelectrolyte complexes is developed. The data on the application of polyelectrolyte complexes of chitosan in medicine and biotechnology, particularly for creation of hemocompatible, thromboresistant materials, bioconstruction materials for replacement of coverlets, blood vessels, bone tissue, immobilisation of biological active compounds, and the non-viral vectors of genetic information transfer are discussed herein. This book investigates polyelectrolyte complexes of chitosan.