The quantum mechanics/molecular mechanics (QM/MM) method is a multi-scale simulation method that is widely used in simulations of realistic materials in which large electronic reorganizations take place (for example enzymatic catalysis, organocatalysis, highly polarized systems). It is particularly suitable when the problem under investigation requires a quantum mechanics treatment of a small region of the system but the environment around the centre can be treated using molecular mechanics. The usage of QM/MM approach requires the knowledge of more features and parametres in the setup than usual simulations. Therefore events where the QM/MM is taught from the basics to applications are very much needed. The goal of the present school is to teach the participants the skills needed to start QM/MM simulations. The emphasis is in biochemical and biological systems, but the same or similar approach can be used in other fields as well.