  The purpose of the ''bootstrap program'' for integrable quantum field
theories in 1+1 dimensions is to construct explicitly a model in terms of its
Wightman functions. In this article, this program is mainly illustrated in
terms of the sinh-Gordon model and the SU(N) Gross-Neveu model. The nested
off-shell Bethe ansatz for an SU(N) factorizing S-matrix is constructed. We
review some previous results on sinh-Gordon form factors and the quantum
operator field equation. The problem of how to sum over intermediate states is
considered in the short distance limit of the two point Wightman function for
the sinh-Gordon model.
