The emergence of powerful handheld devices — coupled with the proliferation of cloud-based applications and an ever-increasing dominance of multimedia content in today’s Internet traffic — have ignited an unprecedented growth of mobile data traffic in recent years. Such a fact has posed significant challenges to mobile network operators, who are now pressed to maintain satisfactory quality of service under exponential traffic demands. To complicate matters, it has also become apparent that traditional approaches to expand network capacity may not suffice (e.g., new spectrum licenses and/or technology upgrades), and they can soon be outpaced by aforementioned traffic growth. Because of that, new ideas to cope with the so-called “data crunch problem” have been sought, and mobile data offloading has appeared as one of the most promising solutions: the routing of macrocellular traffic through alternative networks. Although mobile data offloading is generally thought in terms of WiFi hotspots or femtocell networks, recent developments in the arena of Opportunistic Networks — one of the most interesting evolutions of traditional mobile ad hoc networks (MANETs)  — have paved the way for researchers from both cellular and MANET backgrounds to work together in the development of new network paradigms, architectures, and techniques that can leverage the potentials of both “worlds” to promote and enhance mobile data offloading. Motivated by this vision, we invite researchers, engineers, and practitioners from academia, industry, and the public sector to submit original contributions to the Workshop on CellulAR Traffic Offloading to Opportunistic Networks (CARTOON) 2014. Come and join us in beatiful Philadelphia!