This book offers an analysis of the state-of-the-art in high entropy alloys (HEA). In order to increase the qualities of an alloy, one major element is typically chosen and other elements are added to it in small amounts. In order to create multi-component alloys without a single major element, Professor J.W. Yeh described a novel method of alloy design in 2004. This method involved mixing elements in equiatomic or nearly equiatomic proportions. HEAs have a wide range of structural and physical properties and may find use in various applications. HEAs are intended to have high configurational entropy. The fundamental information now known in the subject, the range of different alloy systems and the features that have been investigated so far, the current major study fields, and the technological applications are presented in this book.