a1 University of Oxford, UK
a2 University of California, Berkeley, USA
a3 Université de Lyon, France
a4 Université Paris Diderot, France
a5 ESO, Garching, Germany
a6 IAC, La Laguna, Spain
a7 MPI for Extraterrestrial Physics, Garching, Germany
a8 Gemini Observatory, Hilo, USA
a9 ASTRON, Dwingeloo, The Netherlands
a10 Universitäts-Sternwarte München, Germany
a11 University of Hertfordshire, Hatfield, UK
a12 The University of Texas, Austin, USA
a13 IAS, Princeton, USA
a14 Leiden University, The Netherlands
a15 New Mexico Tech, Socorro, USA
Early-type galaxies (ETGs) satisfy a now classic scaling relation Re ∝ σ1.2eI−0.8e, the Fundamental Plane (FP; Djorgovski & Davis 1987; Dressler et al. 1987), between their size, stellar velocity dispersion and mean surface brightness. A significant effort has been devoted in the past twenty years to try to understand why the coefficients of the relation are not the ones predicted by the virial theorem Re ∝ σ2eI−1e.