This book presents the history and the evolution of high entropy alloys. It discusses the properties, microstructure, and applications of these alloys. The basic introduction to high entropy alloys and their important effects are also presented. Various metallurgical techniques starting from the traditional to advanced techniques used to prepare high entropy alloys the chances of forming various possible phases and their predictions using different methods are presented. Advanced instruments used to characterize microstructural, mechanical, corrosion, wear, and oxidative resistance are outlined in this book. One of the very important, and commonly used high entropy alloys synthesis methods; ball milling, is also presented. The book includes interesting chapter on electrochemical sensor applications of high entropy alloy powders- a very advanced and new application, useful for detecting toxic dyes, chemicals, and bio-active compounds. Finally, the book presents ‘high entropy oxides’, it’s introduction, properties and applications.