This book aims to provide a practical guide by a set of real world applications of grey systems to social networks, energy management, transportation, natural disaster management, etc. As an emerging subject on data analysis and uncertainty modelling, the theory of grey systems and its applications have seen significant progress in recent years.  However, researchers are still challenged with difficulties in differentiating grey systems from other similar models and a concise and practical guide for their real world applications. This is especially true for researchers in Europe and North American. This book may provide the answer for that. This book is a result of work within the Leverhulme Trust International Research Network on Grey Systems and its Applications. Readers may regard the book as valuable reference in the related fields.