The European Conference on Optics, Optical Systems and Applications, organized by the Optics Division of the European Physical Society, was held in Rome on 7-9 November 1990. The programme consisted of invited and contributed papers which, together with poster presentations, enabled extensive coverage of the subject. The Conference concentrated on nonlinear and nonclassical optics and provided the opportunity for delegates to familiarize themselves with the very latest techniques and developments. ECOOSA 90 - Quantum Optics is an invaluable record of the most up-to-date developments in this rapidly growing field and, as such, will be of use to researchers in all areas of this disciplines.