Magnetic reconnection is the driver of magnetospheric activity. When occuring on the dayside magnetopause, reconnection lets solar wind and interplanetary magnetic flux penetrating the otherwise confined cavity. When occuring on the night side, in the magnetotail, it releases the magnetic energy accumulated over time, into heated and accelerated plasma flows. Kinetic simulations and high resolution in situ observations have allowed for great progress in our understanding of how reconnection works as an isolated plasma process. Little is known however about how reconnection really operates in the complex 3D meso and large scale environement it occurs in. Further progress in that direction is hampered by the difficulties in both modeling numerically collisionless multi-scale systems, and gathering in situ observations, intrinsically local, on a global scale. I will first present results of local kinetic simulations modeling reconnection at the Earth magnetopause. Then I will discuss our current work on developing a new Hybrid Particle-In-Cell code with adaptive mesh refinement to solve larger scale problems. Then and at last, I will present how we exploit decades of multi-missions in situ measurements made in the magnetosphere to better understand the global structure of the dayside magnetosphere.