With the diversity of usage conditions affecting the consumption of multimedia content, the adaptation of dynamic and interactive multimedia presentations is essential. The challenge consists in allowing a multimedia presentation to adapt in all its dimensions: spatially, temporally and interactively, without lessening its attractiveness and still giving the author the control over adapted versions. Additionally, the authoring of adaptable content should not increase the complexity of authoring. To address this challenge, we propose to transpose the concept of scalability to the world of multimedia documents by introducing the so-called Scalable MSTI model. In this paper, we show the properties of this model and how, from an authoring point of view, scalable multimedia documents can be created to address a wide range of usage conditions.