Venom research has focused on front-fanged venomous snakes with fewer than three percent of rear-fanged snake venom proteomes characterised. These venoms have been neglected due to difficulties obtaining venom for characterisation and a lack of toxin sequences in databases for proteomic identifications. We characterized venom gland transcriptomes, venom proteomes, and toxin biological activities, using both enzymatic and toxicity assays, for two Old World and two New World rear-fanged snake species. Venoms were dominated by either three-finger toxins (3FTxs) or metalloproteinases, paralleling the venom dichotomy of front-fanged venomous snakes. Rear-fanged snakes Boiga irregularis and Spilotes sulphureus had venoms dominated by 3FTxs, and shared similar heterodimeric 3FTxs with lizard specific toxicity. In addition, S. sulphureus venom contained a monomeric 3FTx with mammal specific toxicity, allowing this non-constricting snake to capture mammalian prey, whereas B. irregularis uses constriction. Metalloproteinase dominated venoms from Ahaetulla prasina and Borikenophis portoricensis rapidly degraded the alpha subunit of fibrinogen, and within five minutes A. prasina venom also degraded beta subunits. Beta subunit degradation rate for A. prasina was even faster than observed for the front-fanged rattlesnake Crotalus viridis viridis. The majority of bites from rear-fanged venomous snakes do not produce systemic effects in humans, however, these venoms provide insight into toxin binding selectivity and mechanisms of action, as well as predator-prey toxin evolution.