Nowadays, dynamic reconfigurable embedded systems are widely used, since they have the capability to modify their functionalities, adding or removing components and modify interconnections among them. The basic idea behind these systems is to have the system autonomously modify its functionalities according to the application's changes. This paper describes the area of reconfigurable embedded systems presenting both architectural and methodological aspects trying to point out common features and needs. After a brief introduction, an overview of the models, of the reconfigurable architectures, and of the design methodologies will be presented.