From the Introduction: "This resource is provided to inform law enforcement, terrorism prevention practitioners, other first responders, community leaders, as well as the general public about both threats of violence and contextual behaviors that suggest an individual is mobilizing to violence. While some violent extremists may make direct, indirect, or vague threats of violence, others may plot violent action while avoiding such overt threats to maintain operational security--underscoring the need to consider both threats of violence and contextual behaviors. We have incorporated 'unusual' into many of the indicators because we are looking for behavior that is different enough from the individual's normal behavior to cause concern. The indicators included in this booklet are intended to aid law enforcement and first responder investigative and detection efforts, not to be a substitute for their expertise and experience. In addition, we continue to see that members of the community--such as family members and peers--are often best positioned to witness signs of mobilization to violence. Such community members almost always are the first to detect hints that an individual may be considering violent action in the United States or overseas. This booklet is provided to aid interpretation of their observations. This booklet was first published in 2015 and updated in 2017 and 2019."