Cochrane review authors should seek advice from their Trials Search Co-ordinator on sources to search;
CENTRAL is considered to be the best single source of reports of trials for inclusion in Cochrane reviews;
The three bibliographic databases generally considered to be the most important sources to search for studies for inclusion in Cochrane reviews are CENTRAL, MEDLINE and EMBASE;
National, regional and subject-specific databases should be selected for searching according to the topic of the review;
Conference abstracts and other grey literature can be an important source of studies for inclusion in reviews;
Reference lists in other reviews, guidelines, included (and excluded) studies and other related articles should be searched for additional studies;
Efforts should be made to identify unpublished studies;
Ongoing trials should be identified and tracked for possible inclusion in reviews on completion;
Trials registers and trials results registers are an important source of ongoing trials.