• migratory interfaces
• mobile devices
• multimodal interfaces
• user interfaces

The interactive capabilities of portable devices that are nowadays increasingly available, enable mobile computing in diverse contexts. However, in order to fully exploit the potentialities of such technologies and to let end users benefit from them, effective and usable techniques are still needed.
In general, differences in capabilities, such as computational power and interaction resources, lead to an heterogeneity that is sometimes positively referred to as device diversity but also, negatively, as device fragmentation. When designing applications for mobile devices, besides general rules and principles of usability, developers cope with further constraints. Restricted capabilities, due to display size, input modality and computational power, imply important design and implementation choices in order to guarantee usability. In addition, when the application is likely to be used by subjects affected by some impairment, the system has also to comply with accessibility requirements.
The aim of this dissertation is to propose and discuss examples of such techniques, aimed to support user interfaces on mobile devices, by tackling design, development and evaluation of specific solutions for portable terminals as well as for enabling interoperability across diverse devices (including desktops, handhelds, smartphones).
Usefulness and usability aspects are taken into great consideration by the main research questions that drove the activities of the study. With respect the such questions, the three central chapters of the dissertation are respectively aimed at evaluating: hardware/software solutions for edutainment and accessibility in mobile museum guides, visualization strategies for mobile users visiting smart environments, and techniques for user interface migration across diverse devices in multi-user contexts.
Motivations, design, implementation and evaluation about a number of solutions aimed to support several dimensions of user interfaces for mobile devices are widely discussed throughout the dissertation, and some findings are drawn.
Each one of the prototypes described in the following chapters has been entirely developed within the research activities of the laboratory where the author performed his PhD. Most activities were related to tasks of international research projects and the organization of this dissertation reflects their evolution chronology.