Polyelectrolytes and their Applications is the second volume in the series 'Charged and Reactive Polymers'. The important areas of polyelectrolyte applications, i.e., biomedicine, water purification, petroleum recovery and drag reduction, are pre- sented along with discussions of the fundamental principles of polyelectrolyte chem- istry and physics. This book should be of interest to scientists such as physicians, biochemists, polymer chemists and chemical engineers involved in applications of these materials. The first part of the book is devoted to the basic properties of polyelectrolytes in general, namely to the factors influencing the chain conformation of charged polymers in solution and to their counterion selectivity. It also contains methods of synthesis and new concepts of charge stabilized polymer colloids and of polyelectrolyte ca- talysis. The second part describes recent information on the properties and biological effects of already well-known natural polyelectrolytes such as heparin and DNA and recently developed polymers such as pyran and polyionenes. The effects of poly- anions and polycations on normal and transformed cells as well as on acetylcholine receptors follow. This part is of particular interest to scientists involved in biological research.