The US military has an obligation to communicate with the American public, and it is in the national interest to communicate with the international public. Through the responsive release of accurate information and imagery to domestic and international audiences, public affairs (PA) puts operational actions in context, facilitates the development of informed perceptions about military operations, helps undermine adversarial propaganda efforts, and contributes to the achievement of national, strategic, and operational objectives. Information relating to the military and its operations is available to the public from the Department of Defense (DOD) as well as national unofficial sources (e.g., information disseminated by the members, distributed by the public, the media, or by groups hostile to US interests). Regardless of the source, intention, or method of distribution, information in the public domain either contributes to or undermines the achievement of operational objectives. Official information can help create, strengthen, or preserve conditions favorable for the advancement of national interests and policies and mitigate any adverse effects from unofficial, misinformed, or hostile sources. Official communication with internal and external audiences may have a significant effect on the operational environment. Good planning and message development can have a positive impact on operations. Poor planning and message development can turn operational success into strategic failure. It is the responsibility of DOD to make available timely and accurate information so that the public, Congress, and the news media may assess and understand facts about national security and defense strategy. PA activities are divided into public information, command information, and community engagement supported by planning and analysis and assessment throughout the course of operations. This publication provides fundamental principles and guidance for PA support to joint operations. It also addresses PA operations and the role of PA in strategic communication. It adds a discussion of joint PA in domestic operations.