This English translation of a well-known Japanese book covers interfacial physicochemistry in materials science, especially for iron- and steelmaking processes. Interfacial Physical Chemistry of High-Temperature Melts bridges the gap between the basics and applications of physicochemistry. The book begins with an overview of the fundamentals of interfacial physical chemistry and discusses surface tension, describing the derivation of important equations to guide readers to a deep understanding of the phenomenon. The book then goes on to introduce interfacial properties of high-temperature melts, especially the Marangoni effect, and discusses applications to materials processing at high temperature focusing on recent research results by the author and the co-workers.This book is aimed at researchers, graduate students, and professionals in materials processing. Video clips of in-situ observation including experiments under microgravity condition and x-ray observation are available for download on the publisher's website to allow for a deeper understanding.