Space weather has an enormous influence on modern telecommunication systems even though we may not always appreciate it. We shall endeavor throughout this monograph to expose the relationships between space weather factors and the performance (or lack thereof) of telecommunication, navigation, and surveillance systems. Space weather is a rather new term, having found an oMicial expression as the result of several government initiatives that use the term in the title of programs. But it is the logical consequence of the realization that space also has weather, just as the lower atmosphere has weather. While the weather in space will influence space systems that operate in that special environment, it is also true that space weather will influence systems that we understand and use here on terra firma. This brings space weather home as it were. It is not some abstract topic of interest to scientists alone; it is a topic of concern to all of us. I hope to make this clear as the book unfolds. Why have I written this book? First of all, I love the topic. While at the Naval Research Laboratory (NRL), I had the opportunity to do research on many topics including: Thomson scatter radar and satellite beacon studies of the ionosphere, utilization of the NASA Gemini platform for ionospheric investigations, microwave radar propagation studies, I-IF signal intercept and direction-finding experiments, and multi-disciplinary studies of certain physical phenomena relevant to weapon systems development.