Monarch Watch manages a large citizen science effort to tag monarchs from the eastern population during their fall migration, and to recover these tagged butterflies at their overwintering sites in Mexico the following winter. Citizen scientists record the date, location, monarch gender, and unique tag number for each fall-migrating monarch that they tag and then submit these data to Monarch Watch. Tags are recovered in Mexico by residents of the community surrounding the overwintering groves. The data resulting from this collaborative research effort have the potential to answer many important questions regarding monarch biology and conservation. Monarch Watch staff have completed data verification and entry of approximately one million data records, with approximately 200,000 remaining.