Abstract: With the development of IR techniques, contextual information retrieval(CIR) has been identified to be a promising direction for improving search. In CIR, the retrieval of information depends on the time and place of submitting query,history of interaction,task in hand,and many other factors that are not given explicitly but lie implicitly in the interaction and surroundings of searching, namely the context. In this paper, a survey on research work of CIR was given, and the contextual elements of CIR were summarized. In addition, contextual elements were summarized into user context, document context, and system context and the related research work where introduced. At last, the key challen- ges in CIR were discussed from five aspects. Exploitation of real need behind user's query, search based on semantic un-derstanding,contextualinformation retrieval model and et al were pointed out as main problems needed to be resolved.

Key words: Contextual information retrieval, Context, Personalized search, Retrieval model, Semantic understanding