The goal of this project is to investigate in detail the dynamics and composition of the middle and lower atmosphere of Venus by combining data from Venus Express instruments (VIRTIS, VMC) with simultaneous data acquired from several ground-based telescope facilities. The project will perform coordinated observations to provide a detailed analysis of dynamical and chemical couplings between different levels of the atmosphere that are probed simultaneously by different instruments. It is time critical in the context of (1) the extension of the Venus Express (VEx) mission until the end of 2014 and with the possibility of only 1-2 years beyond; (2) the expertise and coordination in wind and trace species measurements developed in our institutions, currently unique in the world; (3) the availability of new techniques of ground-based investigation of Venus' atmosphere, which will benefit from coordination and cross-calibration with in-orbit Venus Express payload instruments.Venus is Earth’s closest sibling, but it has ended up with a radically different climate. Venus atmospheric science is thus increasingly important in an era in which we are trying to understand the divergent evolutionary outcomes for terrestrial planets, whether we are considering the future of our Earth or the habitability in other solar systems. The European Space Agency’s Venus Express is the only spacecraft at Venus – prior to Venus Express, the last Venus orbiter was launched in 1989 – so European scientists now lead the world in Venus research (in marked contrast to the status for most other planets). This project will (a) enhance the legacy of Venus Express data through cross-validation with complementary ground-based telescopic observations; (b) position European ground-based researchers to continue to lead Venus research after the end of the Venus Express mission, and (c) strengthen the position of European researchers in the emerging field of comparative planetology.