Magnetic reconnection underlies important phenomena in nature in a broad range environment, including solar flares, magnetospheric substorms and disruptions in laboratory fusion experiments. The topological change in the magnetic field which occurs during magnetic reconnection requires a breaking of the ideal MHD frozen flux constraint. The present evidence is that collisionless magnetic reconnection can only be understood in the context of a full 3-D system. Given the understanding of the basic physics issues controlling collisionless magnetic reconnection and the numerical tools which are available, the time is ripe to finally solve important magnetic reconnection problems. The proposal will outline an ambitious analytical and computational program to understand collisionless magnetic reconnection in a 3-D system. The role of electron versus ion dynamics in controlling the rate of reconnection, the role of turbulence in breaking up the electron and ion current layers and finally the branching ratio of energy flow from the magnetic field into electrons and ions will be explored. Comparisons will be made to ongoing and past laboratory reconnection experiments as well as satellite observations in the magnetosphere.
