The acronym GIS can be decoded in three distinct ways: GISystems, GIScience, and GIStudies. This framework is used to provide an overarching synthesis, and to ask whether the chapters of the book provide a complete picture of geospatial issues and applications to homeland security. Three characteristics distinguish homeland security applications from other domains: the need for speed; the difficult environments in which technology must operate; and the impossibility of anticipating many relevant kinds of events in either space or time. One of the strongest factors impeding the effective use of geospatial technologies is lack of collaboration between institutions and the cultures of emergency response and GIS. The final section identifies four themes that are largely missing from this book, but nevertheless represent opportunities and challenges for the future.