The study of microquasars, sources in our Galaxy displaying powerful relativistic jets, is a rapidly advancing field in astrophysics. New instrumentation on the ground (MERLIN, SCUBA, VLA, and VLT) and aboard satellites (ASCA, BSAX, ISO, IXAE and RXTE) has provided important results, and much more is expected to come from Chandra and XMM-Newton. In the future, powerful instrumentation will come online in sub-mm (ALMA) and gamma rays (INTEGRAL), extending our coverage to important regions for the study of microquasars. Energy transport via relativistic jets is one of the most important physical mechanisms taking place in compact objects, either in binary systems or in the nuclei of active galaxies. Efforts have been devoted to proper understanding of the disk-jet connection, and even the effects of rotation or magnetic fields. Several important advances have been made, both from the point of view of the theoretical treatment of jets and of observational tests. All of them are reflected in this book.