Epigenetics involves heritable changes in gene expression that do not involve alterations in the DNA sequence. I developed an active-learning approach to convey this topic to students in a college genetics course. I posted a brief summary of the topic before class to stimulate exchange in cooperative groups. During class, we discussed the genotypic and phenotypic differences between monozygotic twins and the role of epigenetic mechanisms in these differences. I also presented the molecular mechanisms that lead to these epigenetic changes as well as techniques used to study them. Students were particularly interested in pondering the relationships between environmental interactions, epigenetic changes, and phenotypic consequences, including human behavior.