In this dissertation we introduce an approach for the authoring of animated transitions in Web applications. The transitions can be defined as navigational state changes that result in the alteration of the presented widgets and interface. These alterations are usually represented abruptly through non-animated interfaces. The use of animation allows a gradual representation of the transformations that occur, characterizing a smooth transition that reveals to the user the underlying navigation operation. The approach is divided in two steps: The interface modeling and the transition modeling. In the first step, we define the interfaces through a specification of abstract interfaces provided by the SHDM/OOHDM method. In the transition modeling, we identify the animations for each transformation and define through the animation rhetorics: The transition rhetorical structure, which defines the animation execution sequence, and the rhetoric styles, that defines the effects and duration proprieties of the animation. The approach was implemented by extending the hypermedia authoring environment, HyperDE, providing smooth transitions for the generated application prototypes. In order to allow the execution of the animations, we have also developed a transition library using Dynamic HTML technology. A preliminary evaluation with users showed greater satisfaction in the use of smooth transitions and a better interpretation of the relations between navigated instances during the interaction process.