The purpose of these activities is to help students to understand the fundamental concepts of gene expression and structure of bacterial operons using as a model the organization and regulation of the lactose operon. Activities range from role-playing the workings of the lac operon to small group "think tanks" to discover and discuss aspects of regulation and control of the operon. In the first and third activities, student groups are assigned one aspect of lac operon regulation and are given the task of acting out the structure and function of the required components. In theother activities, students answer questions about regulation of gene expression through group discussion to promote understanding and application of the concepts. These activities provide visualization, require students to "do and think," and allow for flexible adaptation to many different classroom situations as well as extensions to situations requiring higher-order thinking. This activity was designed to help make the abstract concept of the structure and function of the lactose operon more concrete. Rather than merely memorizing the parts and functions of the operon, students actively participate in the process that they are studying. These activities can then be used to apply knowledge of gene expression in the E. coli lac operon to other operons and other species.