An alloy refers to a mixture of chemical elements, of which at least one is a metal element. After cooling, alloy mixture crystallizes into a solid solution, intermetallic compound or a mixture. Alloys are typically produced to be corrosion-resistant, less brittle, stronger, or to have a more desirable color and luster compared to the constituent metals. They are produced using processes such as electro-deposition method, powder metallurgy, fusion method and the reduction method. The microstructure, chemical composition, and the production technology used to produce the alloys determine the functional properties of alloys. Most commonly, alloys are modeled using the CALPHAD approach, which involves computer coupling of phase diagrams and thermo-chemistry. Brass, white gold, sterling silver, stainless steel, bronze, and 14k gold are some of the prominent examples of alloys. This book aims to shed light on the microstructural aspects, characterization and modeling concepts of alloys. It consists of contributions made by international experts. A number of latest researches have been included to keep the readers up-to-date with the global concepts in this area of study.