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Practicing green chemistry has become more important over the last decade, reflecting the design, development, and implementation of chemical products and processes to reduce or eliminate the use and generation of substances hazardous to human health and the environment. Some of the principles of green chemistry are as follows: 1) It is better to prevent waste than to treat or clean up waste after it has been created. 2) Synthetic methods should be designed to maximize the incorporation of all materials used in the process into the final product. 3) The use of auxiliary substances, solvents, separation agents, and others should be avoided; when used these substances should be innocuous. 4) Employ catalysts or catalytic reagents as selective as possible and that are superior to stoichiometric reagents. Hence, the application of catalysts in chemical reactions and more so the impact of nanostructured catalysts is the scope of this article; a few examples will be discussed pertaining to the topic. A catalyst is considered to be active in any given chemical process if it shows high conversion, is selective to the desired products, is stable for a prolonged period of time, and has good mechanical strength. Out of all the concerns, conversion and selectivity dictate the fate of the catalyst in a larger way as it can significantly change the economics of the process. High conversion can be achieved in general if the catalyst species is not sintered during the reaction and selectivity is achieved from the specific crystal structure of the catalytic active metal or the metal oxide precursor. Hence, controlling the catalyst species at molecular level is possible if catalysts were fabricated at nanometer scale. From the definition, particles of between 1 and 10 nm in size have definite crystal structure at nanometer level, and hence the application of nanostructured materials as catalysts can drastically change the conversion and selectivity in the chemical processes. This article describes in detail how nanostructured catalysts affect the catalytic process in comparison to bulk catalysts. More examples can be found in the book chapter written by Klabunde and Mulukutla.