In contrast to many "ordinary" metals or band insulators, in the case of transition metal oxides the Coulomb interaction between electrons cannot be easily neglected. As a consequence, understanding such systems constitutes a challenge for theorists. At the same time, however, this many–body physics leads to a number of interesting phenomena that can be found in these compounds — such as, e.g., high–temperature superconductivity, magnetic or orbital ordering, or the existence of more or less exotic quasiparticles (spinons, triplons, magnons, etc.).

In this talk, I will give a pedagogical introduction to the physics of one of such quasiparticles — an "orbiton", i.e., a collective excitation in a solid carrying an orbital quantum number. While orbitons had been predicted by theory decades ago, their first unambiguous experimental observation took place only four years ago. Moreover, it has occurred that understanding the properties of the orbiton leads to the introduction of the concept of a separation of electron's spin and orbital quantum numbers.