The XXIII International Youth Scientific School “Coherent Optics and Optical Spectroscopy” (COOS 2019) was held in Kazan, Russia, from October 29 to October 31 on the Tatarstan Academy of Sciences. The School follows the global tendency to comprehensive studies of matter properties and its interaction with electromagnetic fields. Since 1997 more than 100 famous scientists from USA, Germany, Ukraine, Belarus and Russia had plenary lectures presentations. This is the right place, where over 1000 young scientists had an opportunity to participate in hot discussions of the latest scientific news. Many young people have submitted interesting reports on photonics, quantum electronics, laser physics, quantum optics, traditional optical and laser spectroscopy, non-linear optics, material science and nanotechnology. Here we are publishing the full-size papers prepared from the most interesting lectures and reports selected by the Program Committee of the School. Plenary sessions were offered by the following invited speakers: Sergey Kozlov, ITMO University, Saint Petersburg, Russia. • Giant nonlinearity of the refractive index of water in the terahertz spectral range Andrei Naumov, Institute for Spectroscopy RAS, Troitsk, Moscow, Russia. • Optical echo spectroscopy of disordered solid media and composites with quantum dots Renat Gainutdinov, Kazan Federal University, Kazan, Russia. • Quantum electrodynamics in photonic crystals Oleg Khasanov, SPC NAS for materials science, Minsk, Belarus. • Nanocomposites with semiconductor quantum dots: applied aspects and characterization methods Svetlana Kotova, Lebedev Physical Institute, Samara Branch, Samara, Russia. • Vortex light fields in problems of laser manipulation of microscopic objects Andrey Maimistov, National Research University MEPhI, Moscow, Russia. • Nonlinear electromagnetic waves in waveguide arrays and optical plane zones Sergey Sazonov, National Research Center “Kurchatov Institute”, Moscow, Russia. • About optical bullets in a graded-index optical fibers Askhat Basharov, National Research Center “Kurchatov Institute”, Moscow, Russia. • Algebraic perturbation theory and stochastic differential equations in quantum thermodynamics Ivan Popov, Volga State University of Technology, Yoshkar-Ola, Russia. • Detection of trion condensate at room temperature in nanoscale traps on surface defects of the crystal structure of thin filmsList of Program Committee, Organizing Committee and Editorial Board are available in this pdf.