The creation of new and more efficient therapies for improving human health greatly depends on drug delivery systems. Nanotechnology has emerged as a powerful strategy for the development of nanoparticles, such as nanoemulsions, liposomes, nanocrystals, and nanocomplexes, applied in the diagnosis, treatment, or theranostics of several pathologies and diseases. This book reviews the most recent research and development in nanotechnology and, following a multidisciplinary approach, presents new strategies for drug delivery, including aspects from chemistry, physics, biology, and imaging methodologies and exploiting several administration routes, internalization pathways, site-specific delivery strategies, and the potential cytotoxicity of nanoparticles. Beginning with a description of the importance and application of nanotechnology for enhancing existing therapy, the book moves on to detailing oral, topical, pulmonary, brain, cancer, and anti-inflammatory drug delivery approaches; gene delivery approaches; theranostic approaches; and nanoparticle cytotoxicity. Practical and user friendly, it is suitable for advanced undergraduate, graduate, and postgraduate students of nanoscience and nanotechnology; researchers in nanoscience, nanotechnology, chemistry, biology, biochemistry, pharmaceutical sciences, medicine, and bioengineering, especially those with an interest in drug delivery or theranostics; and academia and university readership.