The moduli space of D-branes has a microscopic closed string description in terms of a continuous family of boundary states. Open string field theory provides a new microscopic description in terms of non-perturbative configurations of open strings which solve the open string equation of motion. In this talk, after a general introduction to the subject, I will explain how the SFT parameters are non-trivially related to the boundary state parameters.
We first analyze the relation in the case of a non-perturbative analytic solution and then i present more recent results in Siegel gauge, where we can make contact with string perturbation theory and we can see how SFT takes care of infrared divergences.