The endangered species act a primer congressional research service summary the endangered species act esa pl 93 205 87 stat 884 16 usc 1531 1544 has a stated purpose of conserving species identified as endangered or threatened with extinction and conserving ecosystems on which these species depend the esa is perennially controversial. The endangered species act a primer congressional research service summary the endangered species act esa pl 93 205 87 stat 884 16 usc 1531 1544 has a stated purpose of conserving species identified as endangered or threatened with extinction and conserving ecosystems on which these species depend the esa is perennially controversial. This report discusses the major provisions of the endangered species act both domestic and international and also discusses some of the background issues such as extinction in general and the effectiveness of the statute. The endangered species act a primer congressional research service summary the endangered species act esa pl 93 205 87 stat 884 16 usc 1531 1544 has a stated purpose of conserving species identified as endangered or threatened with extinction and conserving ecosystems on which they depend