Youth wings fulfil vital democratic functions. They connect parties with young people, socialise them into political life, andtrain future candidates and officials. Yet, youth wings have been largely overlooked by party scholars. In this article, wepresent the Youth Wing Membership Survey (YOUMEM) dataset. With responses from over 5000 members of 12 centreleft and centre-right youth wings in Australia, Austria, Germany, Italy, Spain, and Sweden, YOUMEM is the largestcomparative study of youth wing members ever conducted. Using the dataset, we examine some basic questions aboutyouth wing members: who they are, when and why they join. We find that youth wing members are primarily men andhighly educated. Many have relatives who were party members, and most are extremely ambitious compared to seniorparty members. Beyond these commonalities, we also uncover differences across party families and countries. Our projectprovides a unique window on the young people in contemporary youth wings.