The XVII International Feofilov Symposium (IFS2018) continues a sequence of symposia started in 1965. The first nine events were held as national meetings. Already more than 20 years, symposia have been gathering researchers working in the fields of optical spectroscopy and condensed matter physics from all over the world. After the Xth (Saint Petersburg, 1995), XIth (Kazan, 2001), XIIth (Ekaterinburg, 2004), XIIIth (Lake Baikal, 2007), XIVth (St. Petersburg, 2010), XVth (Kazan, 2013) and XVIth (St. Petersburg, 2015) Symposia, IFS2018 will return once again in Ekaterinburg. Optical spectroscopy of crystalline and non-crystalline insulators and semiconductors doped with f- and d-ions; electron-phonon interactions and dynamics; relaxation of excited states; microwave-optical spectroscopy; magnetic resonance spectroscopy; cooperative processes and coherent phenomena; nonlinear spectroscopy; probing of organic and biomaterials; charge transfer phenomena and charge ordering; solid-state lasers, scintillators, phosphors; crystallography aspects for developing of optical materials, and spectroscopy of photonic crystals belong to the main topics of plenary and keynote lectures, oral and poster presentations.