Collective excitations are a central concept in condensed matter physics, tightly related to the notions of phase transitions and broken symmetries widely encountered in materials.
Studying the collective excitations of a material and their coupling to the various available
degrees of freedoms is therefore a crucial step towards a quantitative understanding of its properties and in particular of its phase diagram.
Inthis talk, 1 will review recent experimental progresses in resonant [1) and non-resonant [2) inelastic x-ray scattering methods that now enable the investigation of collective excitations with very high energy resolution. 1 will illustrate fundamental concepts with concretes examples from recent research, focusing in particular on collective lattice (phonons) and magnetic (magnons) excitations.
(1) L. J. P. Ament,et al. Resonant inelastic x-ray scattering studies of elementary excitations, Reviews of Modem Physics 83, 705 (2011).
 A.Q.R. Baron,lntroduction to high resolution inelastic x-ray scattering