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