This book aims to highlight modern methods relating to the synthesis and aqueous solution behavior of ion-containing (co)polymers including both polyelectrolytes and polyzwitterions. From a synthetic standpoint, emphasis is placed on methods for preparing these materials in a controlled fashion, i.e. with pre-determined molecular weights, compositions, and narrow molecular weight distributions. Techniques including atom transfer radical polymerization, reversible addition-fragmentation chain transfer polymerization and ring-opening metathesis polymerization are discussed. Additionally, we highlight the preparation of high molecular weight amphiphilic polyelectrolytes. The aqueous solution properties of both polyelectrolytes and polyzwitterions are likewise discussed. Emphasis is placed on those features unique to particular polymer classes such as the anti-polyelectrolyte effect exhibited by polymeric betaines. Finally certain applications for these ion-containing polymers are highlighted.