We reviewed 180 case studies and a number of theoretical papers on animal relocations published in 12 major international scientific journals over the last 20 years. The study focused on re-introductions, supplementations and translocations (sensu IUCN, 1996. IUCN/SSC Guidelines for Re-introductions. 41st Meeting of the IUCN Council, Gland, Switzerland, May 1995. Http://iuc-n.org/themes/ssc/pubs/policy/hinte.htm.). We did not assess introductions. Re-introductions were the most common type of relocation (116/180); three quarters of these were conducted for conservation purposes. Supplementations (48/180) and translocations (36/180) occurred less frequently, and both were commonly carried out for reasons other than conservation. Simple descriptive statistics were used to analyse factors influencing relocation success. Translocations that aimed to solve human-animal conflicts generally failed. Re-introduction success was not found to have changed over the last two decades, but re-introductions appeared to be more successful when the source population was wild, a large number of animals was released (n > 100), and the cause of original decline was removed. More complex trends were found for the effect of predation and the use of supportive measures such as provision of food or shelter, or predator control prior to release. The success of 47% of re-introductions was uncertain at the time case studies were published in journals. This was partly due to the lack of generally accepted and widely applied criteria to assess success. Very few case studies (3%) reported the cost of the relocation attempt. We conclude that there were three primary aims for animal relocations. These were to solve human-animal conflicts, to restock game populations, and conservation. Our extensive review of the present literature leads us to conclude that the value of animal relocations as a conservation tool could be enhanced through (1) more rigorous testing for the appropriateness of the approach in a given case, (2) the establishment of widely used and generally accepted criteria for judging the success or failure of relocations, (3) better monitoring after a relocation, (4) better financial accountability, and (5) greater effort to publish the results of relocations, even ones that are unsuccessful. (C) 2000 Elsevier Science Ltd.