After the first edition of this book was published at the end of 2003, I was very happy to put the hard work of book writing behind me and concentrate myself with my small team on the development of a multi-functional GPS/Galileo software (MFGsoft). The experiences from the practice and the implementation of the theory and algorithms into the high standard software gave me a strong feeling that I would very much like to revise and to supplement the original book, to modify parts of the contents and to - port on the new progress and knowledge. Furthermore, with the EU Galileo system now being realised and the Russian GLONASS system under development; the GPS theory and algorithms should be re-described so that they are also valid for the Galileo and GLONASS systems. Therefore, I am grateful to all of the readers of this book, whose int- est made it possible so that the Springer asked me to complete this second edition. I remember that I was in a hurry during the last check of the layout of the first edition. The description of a numerical solution of the variation equation in Sect. 11. 5. 1 was added to the book at the last minute in a limited extension of exactly one page.