The New World Mymaridae include 59 genera and subgenera of which 9 are described as new. In addition, 19 species are described. Seven species-groups of Gonatocerus Nees are recognized and four species-groups of Acmopolynema are also proposed. Keys to females and males of the New World genera are provided and keys to subgenera are included under the respective genera. For each genus a diagnosis, synonymy, distribution, and list of known species for the New World are given. Nine described genera and six nominal genera are recorded from the New World for the first time. The book is illustrated with 191 photos and drawings.