In this thesis, atom transfer radical polymerization (ATRP) and reversible addition-fragmentation chain transfer (RAFT) polymerization were utilized in the design of synthetic polymers to create tissue engineering scaffolds and drug delivery systems with improved control over structure and functionality. Thermo-sensitive injectable hydrogels based on poly(NIPAAm) with degradable ester units within the polymer backbone and at the cross-linking sites were prepared using ATRP and RAFT. Solvent induced morphologies of poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) triblock copolymers synthesized by ATRP were described. A micellar structure, composed of a hydrophobic PMMA core and a PEO shell was constructed for delivery of hydrophobic drugs. ATRP was carried out in inverse miniemulsion to prepare well defined functional nanogels that were capable of entrapping and releasing various molecules (Doxorubicin, carbohydrate-based drugs, fluorophores, and gold nanoparticles). The results demonstrated that nanogels prepared by ATRP in inverse miniemulsion could be internalized into cells via clathrin-mediated endocytosis. Nanogels functionalized with integrin-binding peptides increased cellular uptake. A process called Atom Transfer Radical Coupling (ATRC) was also described, which illustrated the power of functionality in ATRP. Finally, linear polymers and cross-linked nanogels were synthesized by ATRP and functionalized with biotin, pyrene, and peptide sequences, tying together the overall themes of structural control and functionality.