Magnetic reconnection is a universal process of rapid energy conversion in plasma. The topology of the magnetic field changes and transfer of magnetic energy into kinetic and thermal energy takes place during the reconnection. Plasma instabilities grown in a thin boundary of plasmas, a thin current sheet, lead to diffusion of magnetic field. As a result magnetic field will be broken and reconnected into another topology. Particles originally trapped in one field line penetrating in the diffusion region will end up in another field line. Due to difference in mass, ions and electrons decouple from the magnetic field under different gradient scales. A certain part of the current sheet undergoing reconnection, where the gradient scale becomes less than the ion scale so that ions are decoupled from the magnetic field, is called the ion diffusion region. There the electrons, still trapped in the magnetic field, produce a distinct electric current pattern and a magnetic field disturbance creates a quadrupolar structure. In this proposed study we investigate the spatial and temporal characteristics of the ion diffusion region in the reconnected current sheet in the in the near-Earth magnetotail. The main aim is to investigate experimentally the properties of the ion diffusion region of reconnection: its structure and evolution. The key question we would like to answer is: How does the ion diffusion region changes in time and space? We plan to quantify the motion and spatial properties of the diffusion region in the current sheet plane, both along the Earth-tail line and along the direction of the currents. We will use the observations from two recent multi-spacecraft missions, Cluster and THEMIS. Based on a statistical study as well as detailed event analysis we investigate the evolution of the reconnection region in the two work packages: WP1 In-situ measurements of ion diffusion region, WP2 Remote sensing of ion diffusion region. The former approach allows us to determine the local characteristics of the ion diffusion region, while the latter approach will identify the large-scale context of the ion diffusion region within the magnetotail. For both work packages we plan to compare the observations of the reconnection with suitable modelling results (analytical and numerical) developed within the proposed research team. We focus on the three dimensional nature of the process, taking into account the locality of the diffusion region in the magnetotail current sheet, which has not been explored in previous experimental studies. Expected results from the analysis include important quantitative parameters of the magnetotail reconnection, such as the spatial scale and motion of the reconnection region. Such parameters are not only important to understand the local energy transfer processes but also the large-scale energy budget in the solar wind-magnetosphere coupling processes.