Alloy refers to a mixture of two or more chemical elements, of which at least one is a metal. Alloy steels are the steels that are made by combining steel with other alloying elements in order to change their properties such as hardness, toughness, strength and wear resistance. Some of the common alloying elements include chromium, nickel, manganese, tungsten and vanadium. Alloy steels are classified into three types including low alloy steels, high alloyed steels and micro-alloyed steels. They are used for producing heating elements for appliances such as pans and pots, toasters, corrosion-resistant containers, and silverware. Alloy steels are also used as skeleton frames in the construction of skyscrapers, bridges, stadiums, and airports. This book explores all the important aspects of alloy steels in the present day scenario. It will also provide interesting topics for research, which interested readers can take up. This book is a resource guide for experts as well as students.