This module contains information for a three part series introducing the venom system in reptiles and discussing it in an evolutionary context. In the first part venom and its ecological roles are defined with a discussion of the diversity of venom structures and venomous lineages, primarily in squamates. Examples are provided of the various ways that venoms may vary among biological scales. In parts 2 and 3, the evolution of venom is discussed. Part 2 focuses on a description of how the venom system arose in squamates and a discussion of the challenges associated with defining "venomousness". Part 3 examines the various genetic mechanisms that produce venom variation using examples from primarily literature that are presented in Part 1. In addition to lecture materials, we include a primary literature based activity and a group activity designed to encourage students to explore the diversity of venomous taxa in reptiles and amphibians.