This book is concerned with functional nanomaterials, materials containing specific, predictable nanostructures whose chemical composition, or interfacial structure enables them to perform a specific job: to destroy, sequester, or detect some material that constitutes an environmental threat. Nanomaterials have a number of features that make them ideally suited for this job: they have a high surface area, high reactivity, easy dispersability, and rapid diffusion,to name a few. The purpose of this book is to showcase how these features can be tailored to address some of the environmental remediation and sensing/detection problems faced by mankind today. A number of leading researchers have contributed to this volume, painting a picture of diverse synthetic strategies, structures, materials, and methods. The intent of this book is to showcase the current state of environmental nanomaterials in such a way as to be useful either as a research resource, or as a graduate level textbook. We have organized this book into sections on nanoparticle-based remediation strategies, nanostructured inorganic materials (e.g. layered materials like the apatites), nanostructured organic/inorganic hybrid materials, and the use of nanomaterials to enhance the performance of sensors.