The articles in this special section focus on ad hoc and wireless sensor networks. The introduction of mobile and sensor-equipped devices has been a revolution for human life, and already we are surrounded by computing, sensing and communication activities. Similar to the problem of how to efficiently communicate among humans, with the introduction of mobile and sensing devices, it became essential to design efficient algorithms to efficiently compute, sense and communicate and to cope with novel issues, such as security and privacy, raised by those new paradigms. In particular, problems such as resource allocations and efficient routing attracted a lot of attention.