Navigation is the science of determining our position and our course of motion. Because it involves such fundamental quantities, navigation has played an essential role in human existence for millennia. This role has hardly diminished, even though we now have the capability to determine where we are with global radio navigation systems such as the Global Positioning System (GPS). If anything, the opposite is true. We are finding new ways of using navigation information to make our travels safer, faster, less costly, and generally more convenient. The field of navigation has undergone extensive changes over the last few decades, due mostly to new satellite capabilities, advances in computers, micro-technology, and better sensors. As a result, it is now possible to determine automatically and nearly instantaneously our position anywhere on Earth, and to use extensive maps and data bases in conjunction with that information to determine where to go and what to do. This holds true whether you are flying in a plane, sailing a ship, riding in a train, traveling by car, or just walking. This ability has far-reaching consequences. Transportation by aircraft or ship is safer than ever. The distribution of goods can be coordinated in a way to achieve maximum efficiency. Even a leisurely drive or walk in the country can benefit from these advances.