Paul Levay and Jenny Craven have amassed, as editors of this book, an impressive, international array of information specialists and librarians together with other information retrieval experts and methodologists from academia, evidence synthesis organizations, libraries and elsewhere with considerable but diverse experience and expertise in systematic searching. In the early days of evidence-based practice, the role of the information specialist or librarian tended to be to help practitioners and researchers to identify systematic reviews and other evidence-based syntheses in the published literature, through searches of bibliographic databases and other related resources. Nowadays, information specialists and librarians serve as expert searchers in efficiently identifying not only systematic reviews but also relevant studies for inclusion in systematic reviews and other evidence syntheses across a wide spectrum of disciplines. The focus on searching for published studies identified solely from bibliographic databases has been replaced with a recognition of the importance of considering unpublished studies and those published in grey literature and the need to use a much wider range of sources, including trials registers, regulatory agency sources and other diverse sources of data. In order to do this, they employ an increasingly diverse and complex range of skills and techniques in both identifying a wider range of resources and exploiting these resources to their full potential, to meet the ever-changing needs of the evidence synthesis community.

Systematic searching is essential for ‘traditional’ systematic reviews within highly-focused research topics and for broader-based topics such as public health, for mixed methods reviews, rapid reviews, realist syntheses, scoping reviews and surveillance, to name but a few. There is a growing recognition of the need for timeliness in evidence syntheses, not only with respect to the amount of time taken to identify the studies and assess their eligibility for inclusion but also with respect to how out-of-date the searches might be at the time of publication of the evidence synthesis. The concept of living systematic reviews and guidelines has been developed to address this, where surveillance techniques are employed to identify studies as soon as their results are made available (either in published or unpublished sources) and the results of the studies are incorporated as quickly as possible into the reviews or guidelines.