The document chronicles the International Labour Organization's (ILO) three-decade journey in addressing the informal sector, beginning with its conceptual roots in the 1950s and 1960s and evolving through various phases of institutional engagement. It highlights accomplishments, challenges, and debates surrounding the definition, measurement, and strategic response to the informal sector, while underscoring its central role in promoting social justice. The paper seeks to provide insights and lessons from history to inform future ILO efforts as they move into a new millennium.