Ecological and distributional data are presented for the 134 species, plus six subspecies, of longhorned beetles (Coleoptera: Cerambycidae) known to occur in Idaho. Species recorded or confirmed for the first time in Idaho are Batyle ignicollis (Say), Brachysomida atra (LeConte), Brachysomida californica (LeConte), Callidium antennatum Casey, Callidium cicatricosum Mannerheim, Callidium hoppingi Linsley, Callimus cyanipennis (LeConte), Clytus canadensis Hopping, Haplidus testaceus LeConte, Hyperplatys aspersa (Say), Judolia gaurotoides (Casey), Leptalia macilenta (Mannerheim), Leptura plagifera LeConte, Megacyllene robiniae (Forster), Meriellum proteus (Kirby), Molorchus longicollis LeConte, Necydalis diversicollis diversicollis Schaeffer, Phymatodes dimidiatus (Kirby), Phymatodes hirtellus (LeConte), Phymatodes nigerrimus Van Dyke, Phymatodes nitidus LeConte, Phymatodes vilitatis Linsley, Poecilobrium chalybeum (LeConte), Saperda horni Joutel, Saperda tridentata (Olivier), Stenocorus nubifer (LeConte), Stenocorus vestitus (Haldeman), and Xylocrius agassizi (LeConte). New adult, larval, or flower host records are given for Cortodera subpilosa (LeConte), Gnathacmaeops pratensis (Laicharting), Grammoptera subargentata (Kirby), Judolia montivagans (Couper), Leptura propinqua Bland, Pseudogaurotina cressoni (Bland), and Trachysida aspersa (LeConte).