  We present an inverse scattering approach to defects in classical integrable
field theories. Integrability is proved systematically by constructing the
generating function of the infinite set of modified integrals of motion. The
contribution of the defect to all orders is explicitely identified in terms of
a defect matrix. The underlying geometric picture is that those defects
correspond to Backlund transformations localized at a given point. A
classification of defect matrices as well as the corresponding defect
conditions is performed. The method is applied to a collection of well-known
integrable models and previous results are recovered (and extended) directly as
special cases. Finally, a brief discussion of the classical $r$-matrix approach
in this context shows the relation to inhomogeneous lattice models and the need
to resort to lattice regularizations of integrable field theories with defects.
