  In this paper we give the boundary string field theory description of
brane-antibrane systems. From the world-sheet action of brane-antibrane systems
we obtain the tachyon potential and discuss the tachyon condensation exactly.
We also find the world-volume action including the gauge fields. Moreover we
determine RR-couplings exactly for non-BPS branes and brane-antibranes. These
couplings are written by superconnections and correspond to K^1(M) and K^0(M)
for the non-BPS branes and brane-antibranes, respectively. We also show that
Myers terms appear if we include the transverse scalars in the boundary sigma
model action.
