Our planet is constantly monitored by hundreds of space-borne instruments. This book describes the technology of those instruments and the sciences that provide useful information from them. It also discusses the political implications of space-borne monitoring. From the moment satellites were launched into orbit their ability to see what was happening on a global scale was appreciated - and feared. This well researched book strives to answer such diverse questions as: Are satellites really a threat to individual privacy? How bad, really, is climate change and global warming? Why can't we find Osama bin Laden? Does the world have enough fresh water?