Article 2(4) of the UN Charter provides that nation-states will refrain from the threat or use of force against the territorial integrity or political independence of any state. It is doubtful whether it will deter states from waging war in cyberspace. Cyber warfare is a perplexing and contentious issue within the ambit of international law. Discussions have focused on whether the existing rules and principles may be extended to cyberspace or whether new treaty law on cyber warfare must be drafted. Against this background the International Group of Experts drafted the Tallinn Manual on the International Law Applicable to Cyber Warfare at the invitation of the NATO Cooperative Cyber Defense Centre of Excellence. The Tallinn Manual provides rules in respect of cyber warfare. In the absence of a multilateral treaty it may be asked whether the Tallinn Manual will achieve acceptance on a global level as rules governing cyber warfare.