Users are currently expected to benefit from the concurrent use of different computing devices and applications: Personal computers for an easier content production, mobile devices for increased mobility and context-awareness, wearable devices for more transparent health-related data acquisitions, etc. However, the simultaneous use of different devices and applications could be perceived as disruptive or unproductive, due to the need of additional settings, lack of integration, etc. As a first step to overcome this problem, in this paper we introduce the notion of Continuous Interaction (CoIn) systems. These systems intend to promote the simultaneous use of multiple devices and applications to complete tasks in a more effective, flexible and easy way. To achieve that goal, a set of human-centred design principles have been figured out to enable users to seamlessly share tasks across multiple devices, independently of the software applications supporting their completion. The case study of a Mobile Forensic Workspace (MFW) will be presented to highlight the benefits that CoIn systems could bring to the Ambient Intelligence (AmI) and Ubiquitous Computing research fields.