This book is a crystallization of the authors’ work over the last twenty-five years. The book covers the latest advances in grey information and systems research, providing a state-of-the-art overview of this important field. Covering the theoretical foundation, fundamental methods and main topics in grey information and systems research, this book includes all the elementary concepts: basic principles, grey numbers and their operations, grey equations and matrices, operators of sequences and generations of grey sequences, grey incidence analysis, grey clusters and grey statistical evaluations, grey systems modeling, grey combined models, grey prediction, grey decisions, grey programming, grey input and output and grey controls, etc. The book will be of interest to advanced students and researchers in a wide range of fields including information and systems sciences and management sciences, and to those working in applied areas such as geo-science, engineering, agriculture, medicine, biosciences and others.