This book is focused primarily on polymer nanocomposites, based on the author's research experience as well as open literature. This text is divided into three parts. Part I – Fundamentals, Processing, and Characterizations - consists of an introduction to nanotechnology, an overview of commonly used nanomaterials, their origins, manufacturing, properties, and current and potential applications as well as the basics of polymer matrices and composites, selection of resin matrix and nanomaterials, processing, and characterizing of multifunctional polymer nanocomposites. Part II – Multifunctional Properties and Applications - consists of seven chapters that discuss the important properties as well as current applications of these polymer nanocomposites. Part III – Concerns and Outlook - consists of two chapters that discuss the environmental and health impacts for nanomaterials and polymer nanocomposites. The environmental health and safety aspects of nanomaterials and polymer nanocomposites, risk assessment and safety standards, and fire toxicity of polymer nanocomposites are studied. In the final chapter, a brief overview of opportunities, trends, and challenges of polymer nanocomposites are included. Throughout the book, the theme is developed that polymer nanocomposites are a whole family of polymeric materials whose properties are capable of being tailored to meet specific applications. This volume serves as a general introduction to students and researchers just entering the field and to scholars from other subfields seeking information.