Mobile ad hoc networks represent a new form of communication consisting of mobile wireless terminals (e.g., handset, PDAs, notebooks). These type of networks are wireless multi-hop packet networks without any fixed infrastructure and centralized administration, in contrast to today’s wireless communications, which is based on a fixed, pre-established infrastructure. The design of wireless ad hoc networks faces many unique challenges. In this article, mobile ad hoc networks and their characteristics are described, and the design issues, applications and future trends of such networks will be discussed.