Development of the elsA software for complex external and internal flow aerodynamics and multidisciplinary applications started in 1997 at Onera. Due to the multi-purpose nature of elsA, many common basic CFD features can be shared by a wide range of aerospace applications: aircraft, helicopters, turbomachinery, missiles, launchers… The elsA software is based on an Object-Oriented design method and on an Object-Oriented implementation based on three programming languages: C++, Fortran and Python. The elsA strategy for interoperability is based on a component approach that relies on standard interfaces for the CFD simulation components. This paper presents an overview of the capabilities of the elsA software in terms of modeling, mesh topology, numerics and boundary conditions, whereas a more detailed description of these capabilities is given in companion papers of this issue of the electronic journal. The importance of High Performance Computing activities is outlined in the present paper.