The number of users of mobile devices has been increasing over recent years, because people have easier and cheaper access to mobile technology, and the cost of mobile Internet access is being reduced. Moreover, usability can be defined as "the measure of the quality of the user experience when interacting with something". This is one of the most important characteristics to be taken into account when addressing systems with a large number of users, who need to operate in an intuitive way, without prior training or direct support. In addition, usability is the second most important problem (after security) for system acceptance by users, so it should not be forgotten when developing systems.

The advantages of usable systems are increased productivity, enhanced quality of work, improved user satisfaction, and reduction in support and training costs. Some studies explore further benefits of usability. Although progress has been made in technological innovations, some obvious limitations still exist on mobile device interfaces due to their characteristics (e.g., small screen size, low-resolution screens, non-traditional input methods, and navigation difficulties). In addition, recently a lot of models of mobile devices of different manufacturers are emerging, which implies that many different input methods (e.g., stick, keyboard, finger, gestures) exist, as well as processing power, size and resolution screen, etc.

The aim of this Special Issue is to collate original research articles and research articles with a focus on mobile usability. We welcome submissions that cover the cognitive, creative, social, health, and ergonomic aspects of interactive mobile computing, which are relevant to the design, analysis, evaluation, and application of innovative mobile interactive systems. Quantitative and qualitative contributions to the theory and applications of mobile human-computer interaction (HCI), as well as work relevant to the theory and practice of innovative mobile interactive systems are also encouraged.

Potential topics include but are not limited to the following:

• Accessibility in mobile information systems
• Ergonomics and human factors considered in mobile devices
• Mobile user experience (UX) and usability in mobile devices
• Innovative interaction techniques in mobile devices
• User interface design and evaluation methodologies in mobile devices
• Design and evaluation of novel interactive systems
• User interface prototyping in mobile devices
• Empirical studies of user behaviour in mobile devices
• Gamification techniques for user interface design
• Intelligent/explainable user interfaces in mobile information systems
• Human language technologies and machine learning in interactive systems
• Interaction in mobile and embedded systems
• Usable security in mobile information systems