  This thesis considers massive field theories in 1+1 dimensions known as
affine Toda quantum field theories. We first consider the boundary sine-Gordon
model, deriving a complete picture of the boundary bound state structure for
general integrable boundary conditions, and then more general ATFTs in the
bulk, discovering a "generalised bootstrap" equation which explicitly encodes
the Lie algebra into the S-matrix. This last is related to a number of S-matrix
identities, as well as a generalisation of the idea that the conserved charges
of the theory form an eigenvector of the Cartan matrix.
