After synthetic zeolites were invented in the 1940s their utility in various applications was recognized early on and has grown tremendously both in breadth and depth of market penetration and their economic impact is reported to be in the trillions of dollars. Application fields include detergents, drying and separation, and a wide variety of catalytic applications, all of which exploit a combination of zeolite features such as ion exchange capacity, high surface areas, pore geometry, and acid–base properties. After giving a brief historical background, this chapter presents a survey of major applications with special emphasis on catalytic applications in the refining, petrochemical, and automotive industries due to their huge economic and societal importance. A major objective here is to attempt to identify key structure types, synthesis, and modification methods and the properties that are critical to performance in various applications in order to provide a sense for what might be fruitful areas of investigation in the search for improved performance or for new applications.