Yemen is in the middle of a major humanitarian crisis, as the country's new transitional government struggles with a southern separatist movement, a threat from al Qaeda militants and a long-running but intermittent conflict in the north.
More than half the population is affected by the crisis. About 10.5 million Yemenis – out of a population of 23 million – do not have enough to eat, and an estimated 13 million have no access to safe water and basic sanitation.
It is the poorest Arab nation, and its economic hardships are aggravated by a lengthy political crisis as well as conflict.
Mass protests began in early 2011 demanding the end of President Ali Abdullah Saleh's 33-year rule and these, combined with growing violence by Islamist and tribal militants, meant the government lost control of whole chunks of the country for several months.
Tens of thousands of people were displaced in southern, central and northern areas. Public services in most of the country stopped, and the unrest created severe fuel shortages and dramatically pushed up the price of food.
The number of malnourished children under the age of five nearly doubled to 750,000 as a result of the political turmoil, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said in February 2012.
The number continued to rise in 2012, and nearly a million children under five are acutely malnourished, the United Nations said in January 2013.
With nearly ;60 percent of children stunted, Yemen has the second highest rate of chronic malnutrition among children after Afghanistan. Stunting – when a child's height is too low for their age – is a sign of longer-term hunger.
Malnutrition is the main cause of death among young children, according to UNICEF.
Many armed groups in Yemen use child soldiers, and during the unrest many more were recruited. In December 2012, the United Nations said children made up an estimated 15 percent of those recruited by pro-government tribal militias, and 20 percent of those recruited by northern Houthi rebels. The Yemeni armed forces have also recruited children. In November 2012, the government banned the recruitment of children by security forces.
Despite an improvement in security in 2012 following the establishment of a unity government, there are still more than 431,000 people displaced within Yemen.
The country is also sheltering 269,000 refugees, mostly from the Horn of Africa, according to U.N. figures published in January 2013. Each year, tens of thousands of people make the treacherous journey across the Gulf of Aden to Yemen - seen as a gateway to wealthier parts of the Middle East and the West.
Yemen has high levels of unemployment, rapid population growth and diminishing water resources.
It is heavily dependent on dwindling oil supplies. But Yemen's oil and gas pipelines have been repeatedly sabotaged by insurgents and tribesmen since the anti-government protests began in 2011, causing fuel shortages and slashing export earnings.
The 2011 protests against President Saleh's rule paralysed the country. Some of his top aides, military commanders, cabinet ministers and diplomats defected to the protesters' side.
In some areas, government forces shot at demonstrators and stopped medical services reaching protest sites, Human Rights Watch said.
Weakened by the protests, the government lost control of swathes of the country. ;Northern rebels carved out their own domain in the north, and al Qaeda militants seized towns in the south.
Fighting involving government forces and rebels, Islamist militants and rival tribesmen affected several parts of the country, mainly the capital Sanaa and the country's southern and northern regions.
Tribesmen attacked and closed the main oil pipeline in the oil-producing Maarib province, near Sanaa, in March 2011. They blew up an empty pipeline in June that year. They blockaded the area, costing the government millions of dollars a day in lost exports and sparking a severe fuel crisis, power outages and soaring prices.
After surviving an assassination attempt in June 2011, Saleh went to Saudi Arabia for medical treatment. Under a deal brokered by the Gulf Cooperation Council, he finally agreed in November to hand over power to his deputy, Vice President Abd-Rabbu Mansour Hadi, and a unity government was formed.
The deal brought some calm to Sanaa, but violence continued in other parts of the country, especially the governorates of Sa'ada and Hajjah in the north, and Abyan and Aden in the south.
In January 2012, parliament granted Saleh full immunity from prosecution.
Presidential elections were held in February, with Hadi as the sole candidate. He is expected to lead Yemen for a two-year interim period leading to parliamentary and presidential elections in 2014.
Al Qaeda-linked militants seized several towns in Abyan governorate from February 2011, including the governorate capital Zinjibar.
Zinjibar was nearly destroyed in clashes between government forces and militants. Tens of thousands fled to other parts of Abyan, the neighbouring Lahij governorate and the southern port city of Aden.
When the situation in Abyan worsened, local tribes began to turn against the Islamists and joined government forces in an effort to push them back, the International Crisis Group (ICG) said.
Saleh held up the Islamists' sudden success as an example of what al Qaeda would do if Yemen slipped further into chaos. But opponents suspected he had given a signal to militants, with whom the government had lines of communication, to make their move because he felt it would strengthen his case with the West for political survival.
In May 2012, after Saleh had stepped down, the government launched a major U.S.-backed offensive and re-gained control of the towns in June 2012.
The Islamist militants and government forces inflicted a "human rights catastrophe" as they vied for control in 2011 and the first half of 2012, ;Amnesty International said. The militants carried out public summary executions, amputations and flogging during their rule, and the military used excessive force as it fought back.
The combination of fighting and human rights abuses displaced an estimated 250,000 people from the southern governorates, particularly Abyan, Amnesty said.
Displacement figures were difficult to verify, because aid agencies were unable to access many displaced people in Abyan and Lahij, and because many were living with relatives or host communities.
Since June 2012, the majority have returned home. But basic services, including water and sanitation facilities, health care and education, as well as law and order, are yet to be restored. Landmines need to be cleared from an area larger than Lebanon, much of it rural land.
The militants called themselves Ansar al-Shari'a (Partisans of Islamic Law) but the name seems to have disappeared from usage. Diplomats in Sanaa said they viewed the group as al Qaeda under another name. Some analysts had suggested it was part of a coalition that included al Qaeda in the Arabian Peninsula (AQAP).
AQAP was formed when the Saudi and Yemeni branches of al Qaeda merged in January 2009. It is based in Yemen, and has carried out a number of suicide bombings since June 2012, targeting military and security facilities and senior officials.
The United States has been using drone strikes against the Islamist militants. But discontent at the use of the unmanned planes has been growing. Armed tribesmen have held protests, saying the strikes kill innocent civilians, and some say they are an infringement of sovereignty.
Meanwhile, separatists are seeking to revive a southern socialist state that Saleh united with the north in 1990. They initially joined the anti-Saleh protesters in 2011, but the two sides later grew apart.
Yemen's unity was troubled from the start and resulted in a short but bloody civil war in 1994. After that many southerners viewed the north as an occupying force, and their sense of marginalisation by the government eventually resulted in a popular protest movement in 2007, which later made calls for separation, ICG said.
Many southerners complain northerners based in the capital Sanaa have discriminated against them and usurped their resources for decades. Most of Yemen's fast-declining oil reserves are in the south. The central government denies allegations of discrimination.
A conflict in Yemen's northern provinces between Shi'ite rebels and the government has raged on and off since 2004, despite ceasefires and pledges of reconstruction. The rebels are known as Houthis after the clan of their leader.
They are adherents of the Zaydi branch of Shi'ite Islam and a strongly tribal minority in mostly Sunni Muslim Yemen. They oppose Yemen's close ties with the United States and say they are defending their villages against government oppression.
Sunni Muslims dominate the government and make up most of Yemen's population. The Zaydis, the closest Shi'ite sect to mainstream Sunni Islam, make up most of the rest.
Fighting escalated in August 2009, raising the total number of displaced by early 2010 to some 250,000 – most of them in Saada governorate, which borders Saudi Arabia and to which outside access was restricted.
Despite a shaky ceasefire deal with the government in February 2010, most of the displaced were reluctant to return home because of continued insecurity, a fear of reprisals and a lack of basic services.
The majority moved into camps. In an arid, drought-prone region, one of the main tasks for aid agencies is providing water.
In October and November 2009, the conflict briefly spread to Saudi Arabia where rebels clashed with Saudi forces, accusing the government there of supporting the Yemeni government in attacks against them. The Saudi government denies this.
The weakening of government control caused by the 2011 protests helped the rebels seize the governorate of Saada.
The Houthis have clashed with northern followers of Salafism, a puritanical brand of Sunni Islam, and with supporters of the powerful Islamist Islah Party. Fighting has come within 50 kilometres (30 miles) of Sanaa.
More than 300,000 people are internally displaced because of conflict between the government and Houthis in Saada, as well as inter-tribal fighting in several northern governorates, the United Nations said in December 2012.
An unknown number of people have sought refuge with friends, relatives or other households in nearby cities or moved away from the region completely. Some had to pay smugglers to get them out.
Saada remains under the control of the Houthis who periodically restrict the movement of aid workers and supplies.
Aid workers have better access to Hajjah and Hudaydah governorates, but they are hampered by illegal checkpoints, tribal conflict and the absence of strong government institutions.
The Yemen Times gives news in English, with detailed reports of clashes and sieges.
The BBC profile includes links to other media.
For the latest U.N. Office for the Coordination of Humanitarian Affairs reports, visit ReliefWeb.
The Carnegie Endowment for International Peace has published research on Yemen.
Human Rights Watch regularly monitors the situation in Yemen.
London's Chatham House also produces occasional briefing papers on Yemen.
The U.N. Children's Fund (UNICEF) tracks the plight of children in conflict-affected areas as well as the country as a whole.
The U.N. Refugee Agency (UNHCR) monitors refugees, and the Internal Displacement Monitoring Centre monitors those displaced by Yemen's internal conflicts.
The World Food Programme (WFP) has useful information about Yemen's food needs.