In recent decades, a number of large, complex human services and public health organizations have developed, which are becoming known as the Fourth Sector. This chapter defines the Fourth Sector, and its large, complex, nonprofit organizations, many of them members of the Alliance for Children and Families. It explores a case study that provides in-depth information about this organization and the work of the Alliance to support the complex organizations among their members. The Fourth Sector presents a unique partnership opportunity for government and must be viewed as a strategic management partner, and operations entity at the state, regional, and national levels. Hillside family of agencies (HFA) strives to improve every aspect of the organization, from business, financial, and human resources to service delivery to youth and families. Through the evolution, and implementation of the strategic intent and data-driven outcomes to inform practice, services are improved on a continual basis.