The chapter introduces the book "Interval-Valued Intuitionistic Fuzzy Sets" by Krassimir T. Atanassov, published as part of the "Studies in Fuzziness and Soft Computing" series. The book covers various aspects of Interval-Valued Intuitionistic Fuzzy Sets (IVIFSs), which were introduced in 1989 as an extension of Intuitionistic Fuzzy Sets (IFSs). The author provides a comprehensive overview of the theory and applications of IVIFSs, including their definition, representability, norms, metrics, relations, operations, and operators. The book also explores the use of IVIFSs in different fields such as graph theory, neural networks, and decision-making processes. The author emphasizes the importance of collecting applied studies on IVIFSs in books and acknowledges the partial support from the National Science Fund of Bulgaria. The book is dedicated to the 150th anniversary of the Bulgarian Academy of Sciences.The chapter introduces the book "Interval-Valued Intuitionistic Fuzzy Sets" by Krassimir T. Atanassov, published as part of the "Studies in Fuzziness and Soft Computing" series. The book covers various aspects of Interval-Valued Intuitionistic Fuzzy Sets (IVIFSs), which were introduced in 1989 as an extension of Intuitionistic Fuzzy Sets (IFSs). The author provides a comprehensive overview of the theory and applications of IVIFSs, including their definition, representability, norms, metrics, relations, operations, and operators. The book also explores the use of IVIFSs in different fields such as graph theory, neural networks, and decision-making processes. The author emphasizes the importance of collecting applied studies on IVIFSs in books and acknowledges the partial support from the National Science Fund of Bulgaria. The book is dedicated to the 150th anniversary of the Bulgarian Academy of Sciences.