Synthesis and design of new nanocatalysts is an important area of research that aims to introduce multiple types of useful applications in a greener market. The necessity of nanostructuring the active sites has emerged as the key point in a successful design of the catalysts. The book covers the progress in this research area done in the last ten years. It includes the classification of catalysts and structure of active sites at the nanoscale. The book covers examples to present the concept, evolution of nanocatalysts from the perspective of chemistry of materials and their applications.