In 2000, the world's leaders joined together in a pledge to radically improve the lives of the poorest people on the planet.
Fifteen years later, how have the UN's Millennium Development Goals (MDGs) - universal primary education, eradicating extreme poverty and hunger, improving maternal health, reducing child mortality and combatting infectious disease - changed the lives of those who live in the town of Mongo in Chad?
Meet the people of Mongo
Set in a dry and dusty landscape, Mongo is a town of 40,000 people, in Chad, a landlocked country in central Africa. Average life expectancy, at 51, is about 30 years lower than in the UK.
Going to school
Kadija, seven, loves hopscotch and reading. When she grows up she wants to be a teacher. Although she has high hopes, her future may well be different.
About 45% of girls in Mongo go to primary school, but many drop out as educating girls is traditionally considered less important than educating boys. Kadija's parents pulled her out of school last year, although now they are sending her again. If she is lucky, she will make it to secondary school - but less than 5% of girls in the region get that far, and by their mid-teens, many are married.
More boys than girls go to school in Mongo, but many are also kept off school to work. Many children aged five to 11 in Chad work for a living. So while there are more schools and teachers compared with 15 years ago, less than 40% of children finish primary school.
More children are completing primary school in Chad, but the girls lag behind the boys
Primary school completion rates
Finding food in the lean times
In the summer months water and food can be hard to come by in central Chad, especially for nomadic villagers such as Ashta. She knows all too well the dangers of hunger, having lost an infant son to chronic malnutrition and diarrhoea.
Ashta cooks for 15 family members every day. Their two daily meals are usually boiled rice in the morning and meat with millet and vegetables later in the day. She is determined to keep her five remaining children alive and regularly sees a local health worker, who can provide medication and high calorie supplements when needed.
Dying from hunger is not unusual in Chad - nearly half of all children in the Guera region, where Mongo is located, suffer from chronic malnutrition - above the national average of 38%. Chad has the third highest child mortality rate in the world: one in six children die before they reach their fifth birthday and malnutrition is one of the main contributing factors.
The percentage of people who are hungry is falling
Population of Chad who are undernourished, (%)
In the past 15 years, the situation has improved, with a steep decline in the percentage of the population that is malnourished, but a high birth rate and growing population has meant there are more children in Mongo suffering from chronic malnutrition.
But the total number of undernourished people is rising
Population of Chad who are undernourished, millions of people
Having a baby
Katrine, 22, has three children to care for. Another baby is on the way, and every month she attends a check-up at the maternity clinic to make sure both she and her unborn child are healthy.
Like many women in Mongo, Katrine has suffered tragedy too - her first baby died when he was less than a year old. She wants to give her new baby the best start in life, so she waits in line for hours at the clinic. "If there was one thing that would make it better, it would be more doctors," she says.
Access to healthcare for women such as Katrine has improved in the past 15 years - with health advice and treatment mainly provided by community health workers at clinics and in home visits.
In Chad, a woman's risk of dying from childbirth during her lifetime was one in eight in 1990. By 2013, this had dropped to one in 15. In the UK, the risk is one in 6,900.
Hassan, 30, is usually seen riding around the streets on Mongo on his motorbike, delivering water. But, two months ago, he started to feel sick and feverish. He went straight to the local health clinic and was diagnosed with malaria.
He was treated quickly with drugs, and after several follow-up visits, he is now recovering. Getting well enough to go back to work is important for Hassan because he has a wife and baby daughter to support.
Otherwise healthy adults can usually recover from malaria with the right treatment but those more at risk are infants. Malaria is still one of the biggest killers of under-fives in Chad and one of the main ways the UN is tackling it is by providing free mosquito nets to the population.
People treated for malaria, 2011-15
Cases in the Guera region of Chad
Source: UN. Data up to May 2015
What changes can Kadija, Ashta, Katrine, Hassan and their families look forward to in the next decade? One of the biggest challenges remains education, according to Dr Aime Namululi, who works for Unicef in Mongo. He has a long list of improvements needed: from better teachers, to more classes and school equipment. "Cultural beliefs that do not favour the education of girls remain a challenge we are tackling at community and government level," he says.
But Dr Namululi says the situtation is getting better and, as the current MDGs expire in 2015, he is proud of the strides that have already been made in terms of free medication for children, mosquito nets and check-ups for pregnant women. He says: "It is my hope that 15 years from now, no children will die from preventable causes."
Video by Suraj Patel. Produced by Laura Cantadori, Steven Connor, Aidan Fewster, Bella Hurrell, James Offer, Nassos Stylianou, John Walton and Marcelo Zanni