Sudan is to hold its first national democratic election in 24 years when voters head for the polls from 11-13 April to elect their next president.
They will also vote for members of the 450-seat National Assembly and governors for the county's 25 states, as well as members of state assemblies.
Voters in the semi-autonomous southern region will additionally elect a president of the South Sudan government and members of its 171-seat Assembly. What is at stake?
When President Omar Hasan al-Bashir seized power following a bloodless coup in 1989, the activities of all political parties and trade unions were frozen for 10 years. Moves towards the restoration of democracy led to the registration of political parties from 1999. Most opposition parties however boycotted the 2000 elections in which Mr Bashir was declared winner amid widespread claims of rigging.
This year's elections are being viewed as a test of the country's ability to function as a democracy. The electoral commission says 15.7m people (81% of all eligible voters) have registered for the election.
However, there have been several calls for the election to be postponed by those who say the country is not ready to hold elections.
Several opposition parties accuse Mr Bashir's National Congress Party of preparing to rig the poll. One main challenger - Yasir Arman from the southern SPLM ex-rebels - has pulled out citing security concerns and fears of fraud.
Mr Bashir is seeking re-election. He faces 11 other presidential candidates including Sadiq al-Mahdi, the man he ousted in 1989.
The president has visibly campaigned in Darfur, where Sadiq al-Mahdi's National Ummah Party historically has strong support.
The UN says pro-government Arab militias have been involved in a campaign of ethnic cleansing against non-Arab locals. Up to 300,000 people have died from the combined effects of war, famine and disease in Darfur, according to the UN.
Mr Bashir is the first sitting head of state for whom an arrest warrant has been issued by the International Criminal Court. He faces seven counts of war crimes and crimes against humanity committed in Darfur. Mr Bashir has vigorously denied the charges.
By March 2010 the government had signed ceasefire deals with two main rebel groups in Darfur. But doubts persist about the level of preparedness for elections in the region, where millions have been displaced by the conflict.
South Sudan referendum
The signing of a peace treaty (the Comprehensive Peace Agreement) in 2005 ended two decades of another civil war between the predominantly Muslim north and the south where most are Christian or follow traditional religions.
The treaty calls for the south and north to equally share the country's rising oil revenue. It also calls for a fairer distribution of power, which led to the creation of a unity government of the former rebel Sudan People's Liberation Movement (SPLM) and the ruling National Congress Party (NCP). Their uneasy partnership has been marked by constant bickering and mutual distrust.
The idea of secession is popular in the south. The President of South Sudan, Salva Kiir, told an African summit in March that a referendum in January 2011 on self-determination for South Sudan was more important than the forthcoming elections.
Although Mr Bashir's party prefers the country to remain united, the president says he will honour the outcome of the referendum. What happens on polling day?
Polling stations will open from 0800-1800 local time (0500-1500 GMT). There are an estimated 16,083 stations throughout the country, with 10,335 of them in the north and 5,748 in the south.
In order to win, a presidential candidate must gain more than 50% of the total votes cast. The result of the presidential poll is expected to be announced on 18 April.
If there is no clear winner, the two leading candidates will enter a second round contest on 10 May. The candidate with the most votes in the run-off wins and the result will be announced the following day.
The president can serve a maximum of two five-year terms. Who are the main candidates?
1) Omar Hasan Ahmad al-Bashir - NCP
President Omar Hasan al-Bashir of the ruling National Congress Party (NCP) was born in 1944 in the Nile River state in the north. He belongs to the al-Ja'alyin people, one of the country's main ethnic groups. His two sons were adopted from southern Sudan.
Mr Bashir joined the army in 1966 and rose quickly through the ranks. When he led fellow officers in a mutiny against Prime Minister Sadiq al-Mahdi in June 1989, he told the nation he wanted "to save the country from rotten political parties". Mr Bashir has led the country ever since. He became Field Marshal Bashir in August 2004.
The NCP, emerged from the Islamist National Islamic Front (NIF) which is opposed to secular law in the country. It was responsible for introducing Sharia in all provinces but the south.
Mr Bashir has two masters degrees in military science from the Sudanese Command College and from Malaysia.
2) Sadiq al-Mahdi - NUP
The 75-year-old candidate for the National Ummah Party (NUP) has twice served as prime minister of Sudan. Sadiq al-Mahdi was only 30 when he became premier in 1966. He resigned the following year after a vote of no-confidence against him in parliament. His second stint as prime minister began in 1986 but was cut short by the 1989 coup.
Mr Mahdi read politics, philosophy and economics at St John's College, Oxford in the UK.
3) Yasir Sa'id Arman - SPLM
Yasir Arman, a northerner, was the presidential candidate for the Sudan People's Liberation Movement (SPLM), the main party in South Sudan, until he announced he was withdrawing from the contest.
He is a Sufi Muslim who broke with tradition to marry the daughter of a traditional leader from southern Sudan.
Born in 1961 in Al-Jazeera State, Mr Arman, like President Bashir, is from the Ja'alyin ethnic group. He studied law at the Cairo University in Khartoum, where he was an active member of the Communist movement. He joined the SPLM in 1986.
4) Salva Kiir Mayardit - SPLM
Salva Kiir Mayardit, chairman of the Sudanese People's Liberation Movement (SPLM), is seeking to retain his position as president of the South Sudan government. He is also Mr Bashir's first vice-president.
Mr Kiir was born in 1951 in the southern Bahr-al-Ghazal state and belongs to South Sudan's largest ethnic group - the Dinka.
He joined the southern "liberation war" in the early 1960s and has also served with the Sudanese national army. In 1983 he joined the SPLM guerrilla movement fighting against the government of Sudan in the second civil war between the north and the south.
Mr Kiir replaced John Garang as president of South Sudan in 2005 following Mr Garang's death in a helicopter crash.
His only challenger, Lam Akol, is standing on the ticket of the splinter SPLM-DC party. What about the legislative race?
A quarter of the more than 2,000 candidates for the National Assembly are standing as independents, as are 107 of the 503 candidates for South Sudan's Legislative Assembly. A large number of candidates for governor of each of the 25 states are also running as independents.
Many voters will be participating in elections for the first time and are likely to find the process complex as it requires voters to complete eight ballots (or up to 12 ballots in the south). These include ballots for district lists, women's lists and local assemblies in addition to ballots for the national and regional leaders (in the case of South Sudan). What about women candidates?
There are 1,051 women candidates representing diverse political parties contesting seats set aside for women in the National Assembly and 2,306 women candidates running for local state assemblies.
They have ignored a fatwa (religious ruling) by Salafist Muslim scholars prohibiting women from standing in the elections. Although Sudan's constitution does not explicitly declare Islam the country's official religion, it says Sharia is the source of legislation in northern Sudan. Who are the observers?
The electoral commission has accredited 250,000 local and international election observers.
The Sudan Domestic Election Monitoring and Observation Programme (a local NGO) is deploying more than 700 observers. The US-based Carter Center is sending 60 observers. There will also be observers from the African Union, the Arab League and the European Union and from China.
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