The purpose of this manual is to provide a broad introduction to the security work of the ITU-T. It is directed towards those who have responsibility for, or an interest in, information and communications security and the related standards, and those who simply need to gain a better understanding of ICT security issues and the corresponding ITU-T Recommendations. This edition establishes some guiding principles which include: • the publication should appeal to a wide audience and should try to avoid complex terminology and terms that are likely to be understood only within specialized domains; • the text should complement, not duplicate, existing material available in other forms (e.g. Recommendations); • it should be written to accommodate publication both as a stand-alone printed document and as an electronic document; • the text should employ web links to Recommendations and other sources of publicly-available material as much as possible. Detailed information, over and above that needed to fulfil the basic objectives should be referenced by web links; and • to the greatest extent possible, the text should focus on work that has been completed and published, rather than work that is planned or in progress. In keeping with these objectives, the manual does not attempt to cover all the ITU-T security work that has either been completed or is underway. Instead, it focuses on key selected topics and provides web links to additional information.