As an emerging computing mode, contextual computing has been drawing more and more attention in both academic and industrial community. With the continuous evolving and maturity of related technologies, such as Internet of things, cloud computing, big data and social computing, contextual computing is growing at a rapid pace. Contextual computing is a computing mode that figures out the required services for particular users by acquiring and analyzing their context information, and provides the corresponding context-aware services actively. This new computing mode brings great comfort and convenience to users’ work and life. In this paper, we present the background of contextual computing together with its key concepts including context information, contextual computing, context-awareness, context-aware system and context-aware service. The important research areas such as context data acquisition, context modelling, context reasoning, active service provision, context-aware middleware, information security and privacy, as well as the relevant technologies are summarized. Finally, we highlight the topics that the further research will focus on in contextual computing based-on the general architecture of contextual computing proposed in this paper.