Fundamentals of Astrodynamics and Applications has become the standard astrodynamics reference for those involved in the business of spaceflight. What sets this book apart is that nearly all of the theoretical mathematics is followed by discussions of practical applications implemented in tested software routines that are available for no additional cost on the web. For example, the book includes a compendium of algorithms that allow students and professionals to determine orbits with high precision using a PC. Without a doubt, when an astrodynamics problem arises in the future, it will continue to be standard practice for engineers to keep this volume close at hand and "look it up in Vallado".While prior editions were exceptionally useful and popular throughout the community, there are a number of reasons why the fourth edition will be even more so. There are many reworked examples and derivations. There is an entirely new chapter on interplanetary motion. There is an improved and expanded discussion of the latest coordinate systems, orbit determination, and differential correction. Perhaps most important is that, as with the third edition, all of the software routines described in the book are now available for free in FORTRAN, PASCAL, C++, VBA, and MatLab. This makes the fourth edition an even more valuable text and superb reference.