After introducing very generally the idea of defect and why they are important, I will review an approach to incorporate them in classical integrable field theories. It is essentially a lagrangian approach in which a defect is implemented as internal boundary conditions on the fields. The various models treated in this way so far (sine-Gordon, nonlinear Schrodinger, Korteweg-de Vries and its modified version) share common features which suggested an underlying general structure. I will propose another approach, directly based on the inverse scattering method, which exhibits these common features in a unified way. The main advantage of this approach is that it allows to discuss integrability in the presence of a defect systematically. It may also simplify the quantization of the models.