This book explores nanoparticles, their chemical and physicals properties, and how they interact in biological systems with proteins, immune systems and targeted cells. Risk assessment of nanoparticles for human use is described, including: cellular paradigms, transcriptomics and toxicogenomics. Finally, the applications of nanoparticles in medicine and antioxidant regenerative therapeutics are presented in several chapters with emphasis on how nanoparticles enhance transport of drugs across biological membrane barriers and, therefore, may enhance drug bioavailability.