Underground warfare was a tactic of yesteryear, but has now re-emerged as more complex and more dangerous than ever before. This book is the first of its kind to examine tunnel warfare in a systematic and comprehensive way, addressing the legal issues while keeping in mind operational and strategic challenges. As in many other aspects of contemporary warfare, the renewed use of the subterranean in armed conflict presents a challenge for many democracies. To Dr. Richemond-Barak, this challenge has not only been under-explored, it is also largely underestimated by the community of states, security experts, and public opinion. She analyzes traditional issues of international humanitarian law as they relate to tunnels and underground operations such as principles of dual use, proportionality, and advanced warning. She also identifies issues that are unique to underground warfare, including complex questions that arise when tunnels are dug underneath a state's own civilian infrastructure and under cultural and religious sites.