  We investigate phase transitions in the Ising model and the ANNNI model in
transverse field using the interface approach. The exact result of the Ising
chain in a transverse field is reproduced. We find that apart from the
interfacial energy, there are two other response functions which show simple
scaling behaviour. For the ANNNI model in a transverse field, the phase diagram
can be fully studied in the region where a ferromagnetic to paramagnetic phase
transition occurs. The other region can be studied partially; the boundary
where the antiphase vanishes can be estimated.
