Machine-to-Machine (M2M) communication is a promising technology for next generation communication systems. This communication paradigm facilitates ubiquitous communications with full mechanical automation, where a large number of intelligent devices connected by wired/wireless links, interact with each other without direct human intervention. As a result, M2M communication finds applications in wide areas such as smart grids, e-healthcare, home area networks, intelligent transportation systems, environmental monitoring, smart cities, and industrial automation. However, distinctive features in M2M communications form different challenges from those in human-to-human communications. These challenges need to be addressed, or otherwise it is not easy for this paradigm to gain trust of people. To understand M2M communications deeply, this paper presents a comprehensive review of M2M communication technology in terms of its system model architecture proposed by different standards developing organizations. This mainly includes 3GPP, ETSI, and oneM2M. Further, we have investigated distinctive features of various M2M applications and their supporting attributes, the M2M data traffic and their characterization, various M2M standardization bodies and their unique tasks, and potential M2M communication challenges and their proposed state-of-the-art solutions, followed by future research directions. 2016 Elsevier Ltd. All rights reserved. ; Scopus