Preparation of functional bio-responsive polymer-based materials is the subject of increasing research efforts. Such type of materials could find broad applications in biology and medicine due to their promising performance in the areas of drug and biomolecule delivery, tissue engineering and diagnostic systems. The preparation of such materials has significantly advanced over last 20 years due to the development of reversible deactivation radical polymerization (RDRP) methods. Atom transfer radical polymerization (ATRP), the most often used RDRP procedure, is a versatile and powerful technique for preparation of various functional polymers. Even though ATRP showed great potential for design and synthesis of materials for biomedical applications, there are still many improvements and innovations that should be made in order to effectively utilize this method for production of useful biomaterials. This dissertation seeks to obtain the information required for improving the understanding of several aspects of ATRP, primarily focusing on controlling the polymerization in aqueous media, and how this contributes to the preparation of materials relevant to the biomedical field. Accordingly, this dissertation is divided into VIII chapters, where Chapter I is an introduction to the ATRP in aqueous media and reviews state of the art of aqueous ATRP and materials prepared by this method. Protein-polymer hybrids (PPH) are commercially available therapeutics for treatment of various diseases. Over the last decade the traditional procedure employed for preparation of PPHs had been “grafting-to”, i.e. attaching a preformed polymer to a biomolecule. This technique was challenged by a new approach “grafting-from”, where a well-defined polymer can be grown directly from a specific site on a biomolecule. This method significantly improves purification procedures and yield, which can potentially bring the cost down. Grafting-from requires performing the polymerization under aqueous conditions, optimally under biocompatible conditions. However, conducting ATRP in homogeneous aqueous media is inherently difficult due to multiple side reactions and high reaction rates.