This book is designed to introduce engineers to the particular challenges of establishing and maintaining tactical networks on the battlefield. It is easy to forget the unique challenges faced in conflict: there is no infrastructure, except what the military force brings with it; there are no cell towers; there is no fibre to the premises. The end users are typically hiding behind the hill, rather than sitting up on top of it, and they can be a few kilometres apart or hundreds of kilometres apart. Networks are ad-hoc and mobile and there is an adversary deliberately trying to jam the signals. Although the technology and the services are similar to their civilian counterpart, establishing and maintaining these networks is an order of magnitude more difficult. The book introduces tactical communications by setting it in a battlefield context. The communication system is there to support commanders in the planning and execution of operations and it must accommodate the commander's battlefield requirements, not constrain his tactical options. Then we review the basic digital communication theory required for wireless data communications and introduce some of the difficulties in implementing these features in the tactical domain. The book then examines existing tactical data architectures, such as Link 16, SINCGARS and EPLRS, and contrasts them with emerging IP waveforms developed through the US JTRS program, such as SRW and WNW. The book then examines satellite communications for beyond-line-of-sight networks and brigade battle management systems, followed by the challenges of installing these systems into military vehicles. A range of issues are covered, from personnel radiation hazard to EMI/EMC issues. Finally, the military electromagnetic environment is hostile so we review the EW threat and describes the basic countermeasures available, and how modern waveforms using spread spectrum techniques can improve network resilience for both analogue and digital communications.