IEEE MASS 2015, the 12th IEEE International Conference on Mobile Ad hoc and Sensor Systems, will be held in Dallas, USA, during Oct 19-22, 2015. Wireless ad hoc communication has applications in a variety of environments, such as conferences, hospitals, battlefields, and disaster-recovery/rescue operations, and is also being actively investigated as an alternative paradigm for Internet connectivity in both urban and rural areas. Wireless sensor and actuator networks are also being deployed for enhancing industrial control processes and supply-chains, and for various forms of environmental monitoring. IEEE MASS 2015 aims at addressing advances in research on multihop ad hoc and sensor networks, covering topics ranging from technology issues to applications and test-bed development.