OSMOSE is a platform for the study and design of complex integrated energy systems. The software is developed in the Laboratory for Industrial Energy Systems (LENI) in the Ecole Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland. The project is motivated by the need of a fexible and performant research tool to study and design energy systems. In this perspective, the general scope of the software is to help the user to develop and compute technology models that combine (a) thermodynamic computations, (b) power and energy integration as well as (c) economic or environomic aspects. OSMOSE , exploits the models by performing (a) sensitivity analysis, (b) optimization and (c) data analysis. The present document is a complete user guide to OSMOSE. In addition, elements of software structure and architecture are exposed. This makes therefore the document useful as an introduction for future developers in the project.