In this book, I will consider the prohibition on the use of force in the context of cyber-attacks (in a broadly defined sense) during peacetime. I will argue that the prohibition on the use of force under Article 2 of the United Nations Charter is in sufficient to regulate the rising phenomenon of cyber-attacks and a bespoke framework for this phenomenon is required. I will further consider whether cyber-attacks are subject to international law. This book’s central contention is that the existing jus ad bellum is inadequate to govern cyber-attacks as this phenomenon presents a challenge that is too complex for the orthodox jus ad bellum analysis.