Global health is the health of populations in the global context;  it has been defined as "the area of study, research and practice that places a priority on improving health and achieving equity in health for all people worldwide".  Problems that transcend national borders or have a global political and economic impact are often emphasized.  Thus, global health is about worldwide health improvement (including mental health), reduction of disparities, and protection against global threats that disregard national borders.  Global health is not to be confused with international health, which is defined as the branch of public health focusing on developing nations and foreign aid efforts by industrialized countries. Global health can be measured as a function of various global diseases and their prevalence in the world and threat to decrease life in the present day.
The predominant agency associated with global health (and international health) is the World Health Organization (WHO). Other important agencies impacting global health include UNICEF and World Food Programme. The United Nations system has also played a part with cross-sectoral actions to address global health and its underlying socioeconomic determinants with the declaration of the Millennium Development Goals and the more recent Sustainable Development Goals.
Global health employs several perspectives that focus on the determinants and distribution of health in international contexts:
- Medicine describes the pathology of diseases and promotes prevention, diagnosis, and treatment.
- Public health emphasizes the health of populations.
- Epidemiology helps identify risk factors and causes of health problems.
- Demography provides data for policy decisions. 
- Economics emphasizes the cost-effectiveness and cost-benefit approaches for the optimal allocation of health resources. 
- Other social sciences such as sociology, development studies, psychology, anthropology, cultural studies, and law can help understand the determinants of health in societies.
Both individuals and organizations working in the domain of global health often face many questions regarding ethical and human rights. Critical examination of the various causes and justifications of health inequities is necessary for the success of proposed solutions. Such issues are discussed at the bi-annual , with experts from WHO and UNESCO, by invitation of the German Ethics Council.
The 19th century held major discoveries in medicine and public health.  The Broad Street cholera outbreak of 1854 was central to the development of modern epidemiology. The microorganisms responsible for malaria and tuberculosis were identified in 1880 and 1882, respectively. The 20th century saw the development of preventive and curative treatments for many diseases, including the BCG vaccine (for tuberculosis) and penicillin in the 1920s. The eradication of smallpox, with the last naturally occurring case recorded in 1977, raised hope that other diseases could be eradicated as well.
Important steps were taken towards global cooperation in health with the formation of the United Nations (UN) and the World Bank Group in 1945, after World War II. In 1948, the member states of the newly formed United Nations gathered to create the World Health Organization. A cholera epidemic that took 20,000 lives in Egypt in 1947 and 1948 helped spur the international community to action.  The WHO published its Model List of Essential Medicines, and the 1978 Alma Ata declaration underlined the importance of primary health care. 
At a United Nations Summit in 2000, member nations declared eight Millennium Development Goals (MDGs), which reflected the major challenges facing human development globally, to be achieved by 2015.  The declaration was matched by unprecedented global investment by donor and recipient countries. According to the UN, these MDGs provided an important framework for development and significant progress has been made in a number of areas.   However, progress has been uneven and some of the MDGs were not fully realized including maternal, newborn and child health and reproductive health.  Building on the MDGs, a new Sustainable Development Agenda with 17 Sustainable Development Goals (SDGs) has been established for the years 2016-2030.  The first goal being an ambitious and historic pledge to end poverty.  On 25 September 2015, the 193 countries of the UN General Assembly adopted the 2030 Development Agenda titled Transforming our world: the 2030 Agenda for Sustainable Development . 
In 2015 a book titled " To Save Humanity " was published, with nearly 100 essays regarding today's most pressing global health issues.  The essays were authored by global figures in politics, science, and advocacy ranging from Bill Clinton to Peter Piot, and addressed a wide range of issues including vaccinations, antimicrobial resistance, health coverage, tobacco use, research methodology, climate change, equity, access to medicine, and media coverage of health research.
Disability-adjusted life years
The DALY is a summary measure that combines the impact of illness, disability, and mortality by measuring the time lived with disability and the time lost due to premature mortality. One DALY can be thought of as one lost year of "healthy" life. The DALY for a disease is the sum of the years of life lost due to premature mortality and the years lost due to disability for incident cases of the health condition.
Quality-adjusted life years
QALYs combine expected survival with expected quality of life into a single number: if an additional year of healthy life is worth a value of one (year), then a year of less healthy life is worth less than one (year). QALY calculations are based on measurements of the value that individuals place on expected years of survival. Measurements can be made in several ways: by techniques that simulate gambles about preferences for alternative states of health, with surveys or analyses that infer willingness to pay for alternative states of health, or through instruments that are based on trading off some or all likely survival time that a medical intervention might provide in order to gain less survival time of higher quality. 
Infant and child mortality
Infant mortality and child mortality for children under age 5 are more specific than DALYs or QALYs in representing the health in the poorest sections of a population, and are thus especially useful when focusing on health equity. 
Morbidity measures include incidence rate, prevalence, and cumulative incidence, with incidence rate referring to the risk of developing a new health condition within a specified period of time. Although sometimes loosely expressed simply as the number of new cases during a time period, morbidity is better expressed as a proportion or a rate.
The diseases and health conditions targeted by global health initiatives are sometimes grouped under " diseases of poverty " versus " diseases of affluence ", although the impact of globalization is increasingly blurring the lines between the two.
Infections of the respiratory tract and middle ear are major causes of morbidity and mortality worldwide.  Some respiratory infections of global significance include tuberculosis, measles, influenza, and pneumonias caused by pneumococci and Haemophilus influenzae . The spread of respiratory infections is exacerbated by crowded conditions, and poverty is associated with more than a 20-fold increase in the relative burden of lung infections. 
Diarrhea is the second most common cause of child mortality worldwide, responsible for 17% of deaths of children under age 5.  Poor sanitation can increase transmission of bacteria and viruses through water, food, utensils, hands, and flies. Dehydration due to diarrhea can be effectively treated through oral rehydration therapy with dramatic reductions in mortality.   Important nutritional measures include the promotion of breastfeeding and zinc supplementation. While hygienic measures alone may be insufficient for the prevention of rotavirus diarrhea,  it can be prevented by a safe and potentially cost-effective vaccine. 
Complications of pregnancy and childbirth are the leading causes of death among women of reproductive age in many developing countries: a woman dies from complications from childbirth approximately every minute.  According to the World Health Organization's 2005 World Health Report, poor maternal conditions are the fourth leading cause of death for women worldwide, after HIV/AIDS, malaria, and tuberculosis.  Most maternal deaths and injuries can be prevented, and such deaths have been largely eradicated in the developed world.  Targets for improving maternal health include increasing the number of deliveries accompanied by skilled birth attendants. 
68 low-income countries tracked by the WHO- and UNICEF-led collaboration Countdown to 2015 are estimated to hold for 97% of worldwide maternal and child deaths. 
Human immunodeficiency virus (HIV) is transmitted through unprotected sex, unclean needles, blood transfusions, and from mother to child during birth or lactation. Globally, HIV is primarily spread through sexual intercourse. The infection damages the immune system, leading to acquired immunodeficiency syndrome (AIDS) and eventually, death. Antiretroviral drugs prolong life and delay the onset of AIDS by minimizing the amount of HIV in the body.
Malaria is a mosquito-borne infectious disease caused by the parasites of the genus Plasmodium . Symptoms may include fever, headaches, chills, and nausea. Each year, there are approximately 500 million cases of malaria worldwide, most commonly among children and pregnant women in developing countries. The use of insecticide-treated bednets is a cost-effective way to reduce deaths from malaria, as is prompt artemisin -based combination therapy, supported by intermittent preventive therapy in pregnancy.
In 2010, about 104 million children were underweight, and undernutrition contributes to about one third of child deaths around the world.  (Undernutrition is not to be confused with malnutrition , which refers to poor proportion of food intake and can thus refer to obesity.)  Undernutrition impairs the immune system, increasing the frequency, severity, and duration of infections (including measles, pneumonia, and diarrhea). Infection can further contribute to malnutrition.  Deficiencies of micronutrient, such as vitamin A, iron, iodine, and zinc, are common worldwide and can compromise intellectual potential, growth, development, and adult productivity.       Interventions to prevent malnutrition include micronutrient supplementation, fortification of basic grocery foods, dietary diversification, hygienic measures to reduce spread of infections, and the promotion of breastfeeding.
Violence against women
Violence against women has been defined as: "physical, sexual and psychological violence occurring in the family and in the general community, including battering, sexual abuse of children, dowry-related violence, rape, female genital mutilation and other traditional practices harmful to women, non-spousal violence and violence related to exploitation, sexual harassment and intimidation at work, in educational institutions and elsewhere, trafficking in women, forced prostitution and violence perpetrated or condoned by the state."  In addition to causing injury, violence may increase "women’s long-term risk of a number of other health problems, including chronic pain, physical disability, drug and alcohol abuse, and depression". 
Although statistics can be difficult to obtain as many cases go unreported, it is estimated that one in every five women faces some form of violence during her lifetime, in some cases leading to serious injury or even death.  Risk factors for being a perpetrator include low education, past exposure to child maltreatment or witnessing violence between parents, harmful use of alcohol, attitudes accepting of violence and gender inequality.  Equality of women has been addressed in the Millennium development goals.
Approximately 80% of deaths linked to non-communicable diseases occur in developing countries.  Increases in refugee urbanization, has led to a growing number of people diagnosed with chronic noncommunicable diseases. 
In September 2011, the United Nations is hosting its first General Assembly Special Summit on the issue of non-communicable diseases. Noting that non-communicable diseases are the cause of some 35 million deaths each year, the international community is being increasingly called to take measures for the prevention and control of chronic diseases and mitigate their impacts on the world population, especially on women, who are usually the primary caregivers.
For example, the rate of type 2 diabetes, associated with obesity, has been on the rise in countries previously plagued by hunger. In low-income countries, the number of individuals with diabetes is expected to increase from 84 million to 228 million by 2030.  Obesity, a preventable condition, is associated with numerous chronic diseases, including cardiovascular conditions, stroke, certain cancers, and respiratory disease. About 16% of the global burden of disease, measured as DALYs, has been accounted for by obesity. 
Neglected tropical diseases
More than one billion people were treated for at least one neglected tropical disease in 2015.  Neglected tropical diseases are a diverse group of infectious diseases that are endemic in tropical and subtropical regions of 149 countries, primarily effecting low and middle income populations in Africa, Asia, and Latin America. They are variously caused by bacteria (Trachoma, Leprosy), viruses (Dengue,  Rabies), protozoa (Human African trypanosomiasis, Chagas), and helminths (Schistosomiasis, Onchocerciasis, Soil transmitted helminths).  The Global Burden of Disease Study concluded that neglected tropical diseases comprehensively contributed to approximately 26.06 million disability-adjusted life years in 2010, as well as significant deleterious economic effects.  In 2011, the World Health Organization launched a 2020 Roadmap for neglected tropical diseases, aiming for the control or elimination of 10 common diseases.  The 2012 London Declaration builds on this initiative, and called on endemic countries and the international community to improve access to clean water and basic sanitation, improved living conditions, vector control, and health education, to reach the 2020 goals.  In 2017, a WHO report cited 'unprecedented progress' against neglected tropical diseases since 2007, especially due to mass drug administration of drugs donated by pharmaceutical companies. 
Global interventions for improved child health and survival include the promotion of breastfeeding, zinc supplementation, vitamin A fortification, salt iodization, hygiene interventions such as hand-washing, vaccinations, and treatments of severe acute malnutrition.   The Global Health Council suggests a list of 32 treatments and health interventions that could potentially save several million lives each year.
Many populations face an "outcome gap", which refers to the gap between members of a population who have access to medical treatment versus those who do not. Countries facing outcome gaps lack sustainable infrastructure. In Guatemala, a subset of the public sector, the Programa de Accessibilidad a los Medicamentos ("Program for Access to Medicines"), had the lowest average availability (25%) compared to the private sector (35%). In the private sector, highest- and lowest-priced medicines were 22.7 and 10.7 times more expensive than international reference prices respectively. Treatments were generally unaffordable, costing as much as 15 days wages for a course of the antibiotic ceftriaxone. The public sector in Pakistan, while having access to medicines at a lower price than international reference prices, has a chronic shortage of and lack of access to basic medicines.
Journalist Laurie Garrett argues that the field of global health is not plagued by a lack of funds, but that more funds do not always translate into positive outcomes. The problem lies in the way these funds are allocated, as they are often disproportionately allocated to alleviating a single disease.