This Thesis presents a theoretical analysis of the operation of magnetic nozzles for plasma space propulsion. The study is based on a two-dimensional, two-fluid model of the supersonic expansion of a hot plasma in a divergent magnetic field. The basic model is extended progressively to include the dominant electron convective terms, the plasma-induced magnetic field, multi-temperature electron populations, and the capability to integrate the plasma flow in the far expansion region. The hyperbolic plasma response is integrated accurately and efficiently with the method of the characteristic lines.Special acknowledgments go to the rest of members of the EP2 (Equipo de Propulsión Espacial por Plasmas) research group at UPM, in particular to my colleague and collaborator Jaume Navarro, with whom I have shared many moments (and coffees). My thanks to all the members of the department, specially Robert Santos, for their friendly support and reassuring presence all along the way. I shall v vi ACKNOWLEDGMENTS not forget my friends from the Physics department, Hodei, Claudio, Gonzalo, Sandra, Antonio, Bayajid, Arnaud, Xin, Juancho, and the rest of my friends at the ETSI Aeronáuticos and elsewhere: you have always managed to make me smile and blow away some stress, and I have always valued the richness in viewpoints of our 'international' group (there are 5 nationalities alone in the people I have named). Laura, Carol, Manu, Pepe, Vero: I am lucky to have met you all and count you among my friends.Marijke Frank deserves a full paragraph just for herself. You have brought life and light to my world, and I could not have probably made this climb without you. You are all sweetness and energy and music. Thank you for the moments we share, and for your support and understanding during my Thesis-journey. Also, thank you for applying your near-native English to correct the introductory Chapters of this text.I want to thank Prof. Manuel Martínez-Sánchez at MIT for the interest he has shown in this Thesis, and for all his intelligent comments on the role of the plasma-induced magnetic field: I value much our discussions, which I hope we will continue to share after this Thesis.I am indebted to Prof. Georg Herdrich, Adam Boxberger and Tomeu Massuti at IRS Stuttgart, Germany, for inviting me to visit their institute for three months and participate in their work. It has been a great learning experience for me. Also, I would like to thank Käthe Dannenmayer and Stéphane Mazouffre at ICARE-CNRS, Orléans, France, for accepting to initiate a comparison of self-similar plasma plume models with their experimental data on two Hall-effect thrusters. Likewise, I deeply appreciate the work done with Claudio Bombardelli, Hodei Urrutxua, and Jesús Peláez, at UPM, and Dejan Petkow and Leopold Summerer, at ESTEC, ESA, regarding the study of the Ion Beam Satellite.Lastly, my thanks go to the members of the Committee for agreeing to review and evaluate my work, and to María García at ETSI Aeronáuticos, who has muddled through the cumbersome bureaucra...