A revision of the genus Aleochara of America north of Mexico is presented. Seven subgenera are redefined with 47 currently recognized species, of which nine are described as new (A. arizonica, A. cavernicola, A. curtidens, A. lobata, A. ocularis, A. nidicola, A. rufobmnnea, A. rufonigra, A. unicolor). The species are arranged according to their relationships into species groups within each subgenus. Sixty-one synonymies are newly established (the first specific name is valid): Subg. COPROCHARA, A. bimaculata Gravenhorst = B. deserticola Casey = B. innocua Casey = B. obsolescens Casey = B. recta Casey; A. notula Erichson = A. duplicata Erichson = B. nanella Casey = B. nitidicollis Casey; A. suffusa (Casey) = B. acuminata Casey = A. verna brundini Bernhauer; A. verna Say = A. alticola Sharp. Subg. XENOCHARA, A. lacertina Sharp = B. salicola Casey = B. imbricata Casey = B. idonea Casey = A. densiventris Bernhauer; A. sallaei Sharp = A. torquata Sharp; A. puberula Klug = B. bipartita Casey; A. fumata Gravenhorst = A. languida Sachse = B. defecta Casey = B. affluens Casey; A. castaneipennis Mannerheim = A. glenorana Casey = B. rotundicollis Casey = B. mannerheimi Casey = B. acomana Casey = B. insulana Casey = B. concurrens Casey = B. eludens Casey = A. oregona Hatch; A. quadrata Sharp = B. uvidula Casey = A. sparsicollis Bernhauer. Subg. CALOCHARA, A. rubripennis Casey = A. rubripes Blatchley = A. wallawallae Hatch. Subg. ALEOCHARA, A. centralis Sharp = A. stygialis Sharp; A. gracilicornis Bernhauer = A. kansana Casey = A. pleuralis Casey = A. americana Casey = A. ellipsicollis Casey; A. lustrica Say = A. pauper Sharp = A. serrata Sharp = A. texana Casey = A. fusicornis Casey = A. sternalis Casey = A. algonquina Casey = A. medialis Casey; A. tahoensis Casey = A. postpicta Casey = A. montanica Casey; A. thoracica Casey = A. collusor Casey. Subg. ECHOCHARA, A. lucifuga (Casey) = A. cavicola (Garman). Subg. EMPLENOTA, A. littoralis (Mäklin) = A. maritima (Casey) = P. arenaria Casey = E. quadrifer Casey = E. trilimbata Casey = E. longiceps Casey. Subg. MASEOCHARA, A. valida LeConte = M. ponderosa Casey = M. robusta Sharp = M. ruficauda Casey; A. opacella (Sharp) = M. hogei Sharp = M. decipiens Casey; A. depressa (Sharp) = M. puberula Casey = M. basalis Casey = M. musta Casey.Ninety-three lectotypes and three neotypes are designated (neotypes are designated for: C. caviola Garman, A. lustrica Say, and A. verna Say).Keys to subgenera and species are provided. All species are described, each illustrated with line drawings and scanning electron microscope photomicrographs, and all available bionomic and distributional data are given. Emphasis was put on host records of those Aleochara species which may be used in biological control of some pest species of Diptera. The systematics and phylogeny of the subgenera and zoogeography of species are discussed.A checklist of Nearctic Aleochara and a table listing the known host records for some species is added.