Introduction At first glance the idea that one could properly describe a computer capability as a weapon is counter-intuitive. There is, indeed, all the difference in the world between the essentially peaceful activity of preparing word files, or Excel spreadsheets or, for that matter, the ubiquitous Powerpoint presentations, and the dropping of bombs, the firing of missiles or the shooting of rifles. The first purpose of this chapter is therefore to discuss whether the notion of cyber weapons makes practical and legal sense and, if so, whether this has implications for the applicability of international law rules. That is the task of the next Section. In Section 3, we consider what, in summary form, the applicable rules of weapons law consist of, noting how some of them would seem to apply to particular kinds of cyber weapon. In Section 4, the obligations of states legally to review new cyber weapons, means and methods of warfare are set forth, and the adjustments to normal processes and criteria that the legal review of cyber weapons seems likely to require are discussed. In Section 5 we seek to draw some conclusions, noting in particular why the application of weapons law to these capabilities is important.