This guide to Laurentian Great Lakes rotifers treats 38 genera, which include 167 taxa. Major emphasis is given to planktonic and near-shore members of the class Monogononta. The guide briefly covers materials and methods used in collecting, preparing and counting rotifer samples, as well as techniques used in examining rotifer trophi and preparing permanent rotifer mounts. Major anatomical identification characteristics of rotifers are also discussed. In addition to a key to genera, keys are given for major species, along with ecological and taxonomic notes. Descriptions for each taxon incorporate photomicrographs, line drawings, and pertinent biometric data. The appendix is a compilation of all rotifers reported for the Great Lakes and includes synonyms, authors and dates of species, and the investigators who reported the species.