This publication makes the case for working with men and women, boys and girls, together in an intentional and mutually reinforcing way that challenges gender norms in the pursuit of improved health and gender equality. In addition to providing a definition for the new concept of gender synchronization, this document provides examples of synchronized approaches that have worked first with women and girls, or first with men and boys, and describes interventions that have worked with both sexes from the start. It also provides examples of new and emerging programs that should be watched in the coming years for the knowledge they may contribute to the implementation of gender synchronization.