Madagascar is one of the world's most recognized biodiversity hotspots and has a diverse assassin bug (Reduviidae) fauna that is still incompletely known, especially for the Ectrichodiinae, or millipede assassin bugs. Ectrichodiinae are a speciose (673 described species, 118 genera), worldwide group of assassin bugs that is most diverse in the Old and New World tropics, but so far only six genera and 10 species have been described from Madagascar. Based on examination of 1981 ectrichodiine specimens mostly from the California Academy of Sciences, as well as a few other collections, dramatic undescribed species-level diversity is revealed. The island's Ectrichodiinae fauna is taxonomically revised with the description of three new genera (Marojejycoris, Tanindrazanus, and Toliarus) and 63 new species: Gibbosella andasibe, Gibbosella betampona, Gibbosella brunalvus, Gibbosella conisimilis, Gibbosella fulva, Gibbosella mantella, Gibbosella megafrons, Gibbosella nitida, Gibbosella notoconica, Gibbosella pallidacorium, Gibbosella pallidalata, Gibbosella planiscutum, Gibbosella quadocris, Gibbosella vangocris, Glymmatophora (Glymmatophora) carolae, Marojejycoris auranticorium, Marojejycoris brevifrons, Marojejycoris francais, Marojejycoris notadichroa, Marojejycoris ranomafana, Tanindrazanus amboasaricus, Tanindrazanus andohahela, Tanindrazanus anjozorobeus, Tanindrazanus antananarivo, Tanindrazanus bemaraha, Tanindrazanus brunneus, Tanindrazanus hannajagodae, Tanindrazanus harinhali, Tanindrazanus irwini, Tanindrazanus joffrevillus, Tanindrazanus kathrynae, Tanindrazanus mahafaly, Tanindrazanus marginatus, Tanindrazanus marojejy, Tanindrazanus nigripes, Tanindrazanus notatus, Tanindrazanus simulans, Tanindrazanus tenebricus, Tanindrazanus varicolor, Tanindrazanus vohiparara, Toliarus karinae, Toliarus trichrous, Toxopus ambohitantely, Toxopus ampitavananima, Toxopus antsiranana, Toxopus basalis, Toxopus brucei, Toxopus farafangana, Toxopus fisheri, Toxopus griswoldi, Toxopus insignis, Toxopus italaviana, Toxopus melobrunneus, Toxopus miandritsara, Toxopus namoroka, Toxopus pallidus, Toxopus parkeri, Toxopus simulans, Toxopus steineri, Toxopus tibialis, Toxopus toamasina, Toxopus toliara, and Toxopus vazimba. Toxopus Bergroth, 1905, is redescribed, with the first description of males in the genus, and Cleptria signoretii Reuter, 1887, is transferred to Toxopus. Gibbosella Chłond, 2010, is also redescribed and includes description of males for the first time. Gibbosella elongata Chłond, 2010, Glymmatophora crassipes Horváth, 1914, and Maraenaspis bidens (Reuter), 1887, are redescribed, with the first description of males for each species. Habitus images, documentation of male and female genitalic features, identification keys, and distribution maps are provided. Males and females are associated based on morphology, geographic information, and, when available, molecular data. The newly discovered species diversity constitutes a sixfold increase over the previously documented millipede assassin bug fauna in Madagascar.--