The Cochrane Collaboration is an international effort to pull together in one place the world's best medical evidence for treatments, diagnostic techniques, and preventive interventions, using the most advanced methods of the rapidly growing science of research synthesis. The reason to do this is to provide a resource that would help ensure that healthcare is based on the best available research evidence ("evidence-based healthcare") in combination with clinical experience. The Collaboration was started in 1993 and now has about 13,000 members in more than 100 countries. The Collaboration's founder (Iain Chalmers in the UK) was knighted in 2000 for this work.

The Collaboration is formally synthesizing (using meta-analysis where possible) the data from intervention studies on similar topics. These syntheses are called systematic reviews and are carried out in such a way that bias is minimized compared to narrative reviews that are common in biomedicine. Cochrane systematic reviews follow a standard scientific format, are produced using special software, and are updated at least every 2 years. The Cochrane Library, which is published quarterly and is available by subscription, now has more than 3,000 systematic reviews.

The Cochrane Collaboration develops several additional healthcare databases and registers that are included in The Cochrane Library. For example, until 2005 the US Center assembled, on behalf of the international Collaboration, all controlled clinical trials that compare two or more interventions and were ever published, anywhere (as of January 1, 2008 there were about 530,000 publications assembled, in Japanese, Chinese, Russian, English and many other languages). As part of this effort, over 2,600 journals are being handsearched page by page by people around the globe. The identified trials are listed in the Cochrane Central Register of Controlled Trials ("CENTRAL"). CENTRAL currently contains well over twice as many trial reports as MEDLINE, the National Library of Medicine's biomedical bibliographic database.

The international Cochrane Collaboration now comprises 12 Cochrane Centers (which provide infrastructure and training), 51 review groups organized roughly by health condition or physiological structure (eg, eyes and vision), 14 fields (cross cutting areas that ensure full coverage of reviews -- eg, child health), 12 methods groups (they develop the methods that we use), and a Consumer Network. There is an elected Steering Group.