The adaptation of user interfaces (UI) is a problem that simultaneously demands a detailed knowledge of man-machine interaction but also knowledge of interactive systems as a whole, going beyond the field of man-machine interaction, to be able to choose from many aspects of information technology, software engineering and distributed systems notably. As shown in this chapter, software engineering and distributed systems deal with software adaptation. However, the human element is often forgotten. This is why, in 1999, we introduced the concept of plasticity of man-machine interfaces to qualify user-centred adaptation. This is the object of this chapter that we will structure in two sections: one to define precisely the concept of UI plasticity and its problem space, the other, in two instalments, dedicated to technical implementation: the frames of reference and our recommendations on how to implement them. We will conclude on this chapter the gains and the problems found.