This introduction presents an overview of the key concepts covered in the subsequent chapters of this book. The book focuses on how the United Nations' (UN) thinking and its doing have evolved, and examines how successfully its ideas and operations have come together. Goals need to recognize and embrace all of development's realities, beyond the merely technical, and emphasize more normative approaches in keeping with the original principles and values of the UN. The book describes where the UN development system (UNDS) came from: its origins and its evolution into a complex and dispersed web of organizations across a wide range of disciplines. The UNDS nevertheless retains key comparative advantages which must be emphasized and to which it must revert. In 1990, the UN Development Programme (UNDP) published its first report on human development, bringing the primacy of the individual back into development thinking. The book also brings the threads together in asking what should come next for the UNDS.