The 7.0 magnitude quake that rocked Haiti on Jan 12, 2010 was the biggest urban disaster in modern history. More than 200,000 people were killed, and another 1.5 million were left homeless.
The tremor struck 15km (10 miles) southwest of the capital Port-au-Prince, and was the most powerful to hit the impoverished country in more than 200 years. It was quickly followed by a series of strong aftershocks of up to 5.9 magnitude.
Thousands of homes, schools and hospitals were destroyed, as well as the U.N. headquarters in Port-au-Prince, the presidential palace and the main prison. Estimates of damage and losses range between $8 and $14 billion.
To make matters worse, a raging cholera epidemic started in October 2010 in an area unaffected by the quake, and spread across the country, killing thousands.
Two years after the quake, more than half a million people are still living in tents and makeshift shelters in Port-au-Prince.
The aid response was hampered from the start by the scale of the devastation. The quake destroyed much of the area's limited infrastructure - the main port was unable to function for several days, roads were destroyed, and there was a massive shortage of fuel to transport relief to the needy.
Those best placed to organise a response - the government, United Nations and aid agencies based in Haiti - had lost staff, offices and computers in the quake.
Thousands of homeless fled to other parts of the country, but many settled in improvised camps around the capital. In the first few weeks after the disaster, the camps lacked food, water, decent shelter and medical care.
An estimated 4,000 people had to have limbs amputated, some because they did not receive medical attention in time.
Security was also a concern. The United States sent thousands of additional troops to help maintain law and order and deliver aid, and the United Nations boosted its peacekeeping force.
In January (2010), the United Nations launched a flash appeal for $575 million in emergency aid. The response was overwhelming, and contributions and pledges poured in. In February, the United Nations launched its largest ever humanitarian appeal for $1.44 billion.
Rescue, medical and relief workers from around the globe began pouring into Haiti hours after the earthquake struck.
Oxfam said the "unprecedented generosity" shown by the world for Haiti saved countless lives by providing water, sanitation, shelter, food aid, and other vital assistance to millions.
The U.N. World Food Programme helped close to 2 million Haitians with school meals, nutrition and cash-and-food-for work programs.
However, the aid operation has also been strongly criticised for a lack of coordination, perhaps not surprising given that the response has brought together a struggling Haitian government, a plethora of U.N. agencies, other governments from around the world and a multitude of charities.
Wary of chronic government corruption, many nongovernmental organisations and aid donors set their own priorities, often with little coordination. ; ;
Of the thousands of charities working in Haiti, only a few hundred formally registered with the government and sent reports to the planning ministry as required by law.
Former Prime Minister Jean-Max Bellerive often complained that many charities in Haiti bypass the government in their operations, some offering no reporting or accountability at all.
Before leaving Haiti in late 2010, the former Organization of American States representative Ricardo Seitenfus accused some humanitarian organisations of using the country as a "laboratory" and an opportunity to "do business".
The BBC reported that some people simply could afford to leave the camps because foreign aid workers pushed up rents.
In January 2011, Jean Renald Clerisme, who had one of Haiti's best paid jobs as senior adviser to then President Rene Preval, said he was being asked $2,000 for rent on a house he wanted to move to - more than half his salary.
"When you have foreigners, the price goes up and the local cannot afford to pay," he told the BBC.
Aside from pushing up rents, Clerisme said foreign aid workers were actually encouraging more people to live in camps by concentrating nearly all their services around them.
Others say the influx of medical charities undermined Haiti's healthcare system with many medical staff quitting to take up better paid jobs with international agencies. The availability of free medical care meanwhile forced pharmacists out of business and doctors lost their patients.
An influx of free food similarly undercut local agriculture, according to Oxfam.
Many aid groups are now shifting gears from offering emergency aid to longer-term development projects.
The pressing issue is how to provide solid shelter for the homeless.
The United Nations estimates that 70,000 buildings collapsed and tens of thousands more were damaged, creating an estimated 10 million cubic metres of rubble – enough to fill 4,000 Olympic-sized swimming pools.
More than half of the rubble had been cleared by January 2012, much of it done by hand on hillsides and densely populated areas of the capital that were inaccessible to heavy machinery.
The aid operation involves about 12,000 aid groups. Then Prime Minister Gary Conille said in January 2012 that it was too scattered and lacked coordination.
Around half a million people are still homeless, most of them living in overcrowded camps dotted around the city. Many have no running water or electricity.
Rape is a major problem. Armed gangs roam the camps after dark, often breaking into tents or attacking girls and women when they go to the toilet. ;Local rights groups point to poor or non-existent lighting, overcrowding and little police presence.
Although the number of tent camps has fallen, it has not translated into new, permanent housing for many. Thousands of quake victims have been relocated after accepting cash and other assistance from aid groups, and many have been forcibly evicted by landowners. ; Many are now living in densely packed slums.
The rebuilding process is hampered by disputes over land ownership which may take years to resolve.
Before building work can even start, the government and aid agencies need to determine who owns what land - a major challenge after the earthquake killed some 16,000 civil servants and destroyed title deeds and land registry records.
Even before the quake, land ownership was a thorny issue in Haiti, contributing to violence and poverty in a country where land is concentrated in the hands of a few big landowners, known as grandons.
Few Haitians own land titles and there is no proper land registry system, with most titles passed down orally from one generation to the next.
Haiti's recovery has also been affected by its first cholera outbreak in decades, which began in October 2010 in an area unaffected by the earthquake and quickly spread across the country. By January 2011, it had killed 3,600 people, and a year later 7,000 people had died and 500,000 been infected.
A disputed presidential election in 2011 and a political crisis that later deprived President Michel Martelly of a working government for months, have also complicated the reconstruction efforts.
Many worry not enough is being done to provide Haitians with jobs and address deeply-rooted problems like education that could help Haiti pull itself out of crushing poverty and underdevelopment.
Damages and losses from the Haitian earthquake were evaluated at $7.9 billion, according to the World Bank, although estimates from other sources give higher figures.
At a major donors' conference in New York in March 2010, donors pledged $9 billion to support Haiti's five-year reconstruction and development plan.
A disaster management body was set up in April, co-chaired by former U.S. President Bill Clinton, the U.N. special envoy for Haiti, and by Prime Minister Bellerive.
The Interim Haiti Recovery Commission decided which reconstruction projects to fund, and was due to operate for 18 months before handing over to a government redevelopment authority. The money is being administered through a Multi-Donor Trust Fund, supervised by the World Bank.
However, the IHRC did not establish its successor in time and, in March 2012, President Martelly was still trying to get parliamentary approval to extend IHRC's mandate which had expired in October 2011.
By December 2011, the international community had delivered over half of the pledges intended for reconstruction in 2010 and 2011, according to the World Bank.
One major concern for donors is corruption which is rife in Haiti, particularly in the construction sector.
Threat of more tremors
Haiti faces a threat of further earthquakes. One of the geophysicists who warned Haitian officials in 2008 there could be a 7.2 magnitude quake on the horizon has said another major earthquake may be triggered by January's tremor.
U.N. experts and aid agencies have urged the government and donors to commit to building earthquake and hurricane-resistant schools, hospitals and houses. They say this would add less than 10 percent to building costs and save countless lives in the future.
Before the quake, Haiti's sprawling capital was littered with shoddy buildings due to poor construction standards and inadequate building regulations. Many homes were built on steep slopes and unstable foundations.
Training people to protect themselves during an earthquake can also save lives. Many in Haiti did not know the safest places to go, and some were killed in the aftershocks because they did not leave their buildings after the first quake struck.
For more on Haiti's troubles, see our briefing on the country's violent past.
Click here to see our multimedia documentary marking the one year anniversary.