Opportunistic networking, by definition, allows devices to communicate whenever a window of opportunity is available. Many emerging technologies employ opportunistic exchanges of information. This book addresses this trend in communications engineering, taking into account three specific areas?vehicular, device-to-device (D2D), and cognitive radio?while describing the opportunistic communication methods of each. From smart homes to smart cities, smart agriculture to never-die-networks and beyond, the text explores the state of the art of opportunistic networking, providing the latest research, developments, and practices in one concise source.