The "Under the Mistletoe" project was developed to capitalize on student curiosity about the American Christmas Mistletoe plant and draw learners into an engaging, inquiry-based exercise that incorporates numerous life science standards and collaborative research. By collecting data on host and nonhost tree size, location, and number of mistletoe present during the winter months--after the trees have lost their leaves--students investigate the host-parasite relationships of mistletoe. Students gain experience developing research questions, using scientific equipment to collect data, and drawing conclusions based on the integration of math and science. (Contains 4 figures.)