World Health Organization is the United Nations specialized agency for health and centre of leading international cooperation for more than 60 years. The work of WHO is governed by the World Health Assembly and Executive Board and is carried out by the Secretariat.

The constitution of the World Health Organization defines health as its first principle:

WHO's roles and mandates under its Constitution and guidance provided by its governing bodies WHO is the directing and coordinating authority for health within the United Nations system and is responsible for providing leadership on global health matters. In its work, WHO takes international law into consideration in its entirety. In addition to the international drug conventions, WHO's work related to narcotics and psychoactive substances is guided by the WHO Constitution and by the Organization's governing bodies – chiefly through resolutions of the World Health Assembly and WHO's regional committees.

WHO fulfils its objectives through its core functions:
Providing leadership on matters critical to health and engaging in partnerships where joint action is needed; shaping the research agenda and stimulating the generation, translation and dissemination of valuable knowledge; setting norms and standards and promoting and monitoring their implementation; articulating ethical and evidence-based policy options; providing technical support, catalysing change, and building sustainable institutional capacity; and monitoring the health situation and assessing health trends.

To understand the mandate properly of the World Health Organization one can refer to the link below to go through the WHO constitution once