Living Review in Solar Physics for the invitation to write this review and the support all along the manuscript preparation. The author thanks Jean-Claude Vial and Nicolas Labrosse for their comments on the first draft of the manuscript, and Giannina Poletto for the time she dedicated to improve a later version of it. The author is also grateful to Andrei Zhukov for the discussion. Sincere thanks go to Judy Karpen and the second anonymous referee for their extremely valuable comments and suggestions. Acknowledgments go the ISSI team “Solar prominence formation and equilibrium: new data, new models” for the stimulating discussions, and the Institut d’Astrophysique Spatiale (IAS, France) for the support. The author acknowledges the financial support from the Belgian Federal Science Policy Office through the international cooperation programs and the ESA-PRODEX program.