All of the organizations described in the S&S Guide are engaged in important and interesting activities related to security and/or sustainability. But some appear more important or interesting than others. The Guide tries to identify centers of expertise and leading-edge thought and action in all areas of security and sustainability. This is no easy matter, and opinions will surely differ as to which organizations deserve highlighting. Still, as an initial introduction to the organizations covered in the Guide, most of the following selections should be of interest to most users. Emphasis has been given to those organizations emphasizing security and sustainability, and/or taking a broad systems approach to global concerns.