Malicious cyber activities are becoming more and more commonplace, including between nations. This has caused great speculation as to the rules that govern military cyber operations, particularly during armed conflict. The upcoming publication of the Tallinn Manual on the International Law Applicable to Cyber Warfare is indicative of the importance of this discussion. This article analyzes the application of the law of armed conflict principles of proportionality and precautions to cyber operations, including reference to the Tallinn Manual. In most cases, the existing law provides a clear paradigm to govern cyber activities. However, this article identifies several areas where governments and military operators might question how to apply these principles to a specific cyber operation. In these areas, greater precision is needed to provide clear guidance to those who plan, order, and conduct cyber operations.