  We review our recent results on the on-shell description of sine-Gordon model
with integrable boundary conditions. We determined the spectrum of boundary
states by closing the boundary bootstrap and gave a derivation of Al.B.
Zamolodchikov's (unpublished) formulae for the boundary energy and the relation
between the Lagrangian (ultraviolet) and bootstrap (infrared) parameters. These
results have been checked against numerical finite volume spectra coming from
the truncated conformal space approach. We find an entirely consistent picture
and strong evidence for the validity of the conjectured spectrum and scattering
amplitudes, which together give a complete description of the boundary
sine-Gordon theory on mass shell.
