Homosexuality is romantic attraction, sexual attraction, or sexual behavior between members of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" to people of the same sex. It "also refers to a person's sense of identity based on those attractions, related behaviors, and membership in a community of others who share those attractions."Along with bisexuality and heterosexuality, homosexuality is one of the three main categories of sexual orientation within the heterosexualhomosexual continuum. Scientists do not yet know the exact cause of sexual orientation, but they theorize that it is caused by a complex interplay of genetic, hormonal, and environmental influences and do not view it as a choice. Although no single theory on the cause of sexual orientation has yet gained widespread support, scientists favor biologically based theories. There is considerably more evidence supporting nonsocial, biological causes of sexual orientation than social ones, especially for males. There is no substantive evidence which suggests parenting or early childhood experiences play a role with regard to sexual orientation. While some people believe that homosexual activity is unnatural, scientific research shows that homosexuality is a normal and natural variation in human sexuality and is not in and of itself a source of negative psychological effects. There is insufficient evidence to support the use of psychological interventions to change sexual orientation.The most common adjectives for homosexual people are lesbian for females and gay for males, but the term gay also commonly refers to both homosexual females and males. The percentage of people who are gay or lesbian and the proportion of people who are in same-sex romantic relationships or have had same-sex sexual experiences are difficult for researchers to estimate reliably for a variety of reasons, including many gay and lesbian people not openly identifying as such due to prejudice or discrimination such as homophobia and heterosexism. Homosexual behavior has also been documented in many non-human animal species, though homosexual orientation is not significantly observed in other animals.Many gay and lesbian people are in committed same-sex relationships. These relationships are equivalent to heterosexual relationships in essential psychological respects. Homosexual relationships and acts have been admired, as well as condemned, throughout recorded history, depending on the form they took and the culture in which they occurred. Since the end of the 20th century, there has been a global movement towards freedom and equality for gay people, including the introduction of anti-bullying legislation to protect gay children at school, legislation ensuring non-discrimination, equal ability to serve in the military, equal access to health care, equal ability to adopt and parent, and the establishment of marriage equality.

The World Health Organization (WHO) is a specialized agency of the United Nations responsible for international public health. The WHO Constitution states its main objective as "the attainment by all peoples of the highest possible level of health". Headquartered in Geneva, Switzerland, it has six regional offices and 150 field offices worldwide.

The WHO was established on 7 April 1948. The first meeting of the World Health Assembly (WHA), the agency's governing body, took place on 24 July of that year. The WHO incorporated the assets, personnel, and duties of the League of Nations' Health Organization and the Office International d'Hygiène Publique, including the International Classification of Diseases (ICD). Its work began in earnest in 1951 after a significant infusion of financial and technical resources.The WHO's mandate seeks and includes: working worldwide to promote health, keeping the world safe, and serve the vulnerable. It advocates that a billion more people should have: universal health care coverage, engagement with the monitoring of public health risks, coordinating responses to health emergencies, and promoting health and well-being. It provides technical assistance to countries, sets international health standards, and collects data on global health issues. A publication, the World Health Report, provides assessments of worldwide health topics. The WHO also serves as a forum for discussions of health issues.The WHO has played a leading role in several public health achievements, most notably the eradication of smallpox, the near-eradication of polio, and the development of an Ebola vaccine. Its current priorities include communicable diseases, particularly HIV/AIDS, Ebola, COVID-19, malaria and tuberculosis; non-communicable diseases such as heart disease and cancer; healthy diet, nutrition, and food security; occupational health; and substance abuse. Its World Health Assembly, the agency's decision-making body, elects and advises an executive board made up of 34 health specialists. It selects the director-general, sets goals and priorities, and approves the budget and activities. The director-general is Tedros Adhanom Ghebreyesus of Ethiopia.The WHO relies on contributions from member states (both assessed and voluntary) and private donors for funding. Its total approved budget for 2020–2021 is over $7.2 billion, of which the majority comes from voluntary contributions from member states. Contributions are assessed by a formula that includes GDP per capita. Among the largest contributors were Germany (which contributed 12.18% of the budget), the Bill & Melinda Gates Foundation (11.65%), and the United States (7.85%).Since the late 20th century, the rise of new actors engaged in global health such as the World Bank, the Bill and Melinda Gates Foundation, the US President's Emergency Plan for AIDS Relief (PEPFAR) and dozens of public-private partnerships for global health have weakened the WHO’s role as a coordinator and policy leader in the field.