Today, concerns over homeland security have led thousands of Americans to volunteer for various citizen emergency response groups, such as the Civil Air Patrol, U.S. Coast Guard Auxiliary, Community Emergency Response Teams, fire units, etc.  In Citizens Defending America, Martin Greenberg focuses new attention on the subject of citizen volunteerism by chronicling the nature and purpose of volunteer police units—authorized organizations of a public or private nature that work at deterring crime and/or preventing terrorism for little or no monetary compensation—in America since 1620.  A number of these historical groups responsible for maintaining the civil order of the day—slave patrols, frontier posses, vice suppression societies, the American Protective League, for example—now seem controversial when viewed through a contemporary lens.  Greenberg uses the history of such groups to reflect upon the nation’s past and to consider the possibilities for a safe and secure future.  He also emphasizes the role of young people in the fields of security and safety, and stresses the need for more qualified, trained volunteers to help cope with man-made and natural disasters.