This book gives a thorough and systematic introduction to the latest research results on hesitant fuzzy and its extensions decision making theory. It includes five chapters: Hesitant Fuzzy Set and its Extensions, Distance Measures for Hesitant Fuzzy Sets and Their Extensions, Similarity Measures for Hesitant Fuzzy Sets and Their Extensions, Entropy Measures for Hesitant Fuzzy Sets and Their Extensions, and Application of Information Measures in Multiple Criteria Decision Making. These methodologies are also implemented in various fields such as decision making, medical diagnosis, cluster analysis, environmental management, etc. This book is suitable for the engineers, technicians, and researchers in the fields of fuzzy mathematics, operations research, information science and management science and engineering, etc. It can also be used as a textbook for postgraduate and senior-year undergraduate students of the relevant professional institutions of higher learning.