Chartered in 1921, the Service Employees International Union (SEIU) is a worldwide organization that represents more than two million workers in occupations from healthcare and government service to custodians and taxi drivers. Women form more than half the membership while people in minority groups make up approximately forty percent. Luis LM Aguiar and Joseph A. McCartin edit essays on one of contemporary labor's bedrock organizations. The contributors explore key episodes, themes, and features in the union's recent history and evaluate SEIU as a union with global aspirations and impact. The first section traces the SEIU's growth in the last and current centuries.