Sudanese voters are going to the polls for the first time since the end of a 21-year north-south conflict which left some 1.5 million people dead.
However, a separate conflict is still underway in the western region of Darfur. BBC correspondents around the country describe the scene at the start of the three-day process.
JAMES COPNALL, KHARTOUM
At Unity School in Khartoum a man with a pristine white turban wrapped round his head explained how he had waited a quarter of a century to vote.
"I took part in the election in 1986, but after that I lost interest in politics," said the man, who refused to give his name.
Now he has the chance to vote; and he arrived at the polling station before it even opened to make sure he could perform his civic duty.
First multi-party polls in 24 years
Polls to elect president and 450-member national assembly, as well as governors and legislative bodies for 25 states
Complicated process, with some in the south having to cast 12 different votes
Several opposition parties have boycotted the polls, alleging fraud
Results to be announced 18 April
Southern Sudan due to hold independence referendum in January 2011
But he, like others elsewhere in the country, had to wait.
These are extremely complicated elections - voters in the north have to vote eight times, and those in the south 12 times.
One of the eight ballot papers had not arrived, so there was a delay before voting got under way.
A line of women in headscarves sat patiently in the shade.
When I asked if they were enjoying the elections, they grinned shyly, and gave big thumbs up signs.
One voter said she was delighted with the diversity of people she saw around her, as Sudanese go to the polls for the first time in many people's lifetimes.
"I feel happy about all the people, women with men, young, the soldiers with the civilians, with all the people around, really I am very happy," said Fawzi Ahmed Mirghani.
Next door, President Omar al-Bashir's National Congress Party had set up a makeshift office in a school playground.
Voters were being talked through the process they would follow once they went to the polling station.
It is perhaps a small sign of the advantage enjoyed by the party in power.
Elsewhere in Khartoum it was reported that soldiers and others were bussed in to vote.
Already rights groups and opposition party activists say they have discovered evidence of rigging.
The National Elections Commission has warned that no elections are perfect.
The key question now is: How widespread and on what scale are the irregularities?
WILL ROSS, JUBA
Things got off to a slow, somewhat bizarre start at Kololo polling station in central Juba where Salva Kiir, President of Southern Sudan was to vote.
As the blaring police sirens announced his arrival, the electoral officers were busy assembling the flat-packed cardboard polling booths.
Voters in the south are taking part in 12 contests
Mr Kiir, in his trademark black cowboy hat, observed the scene and wisely decided to take a seat.
More than half an hour later he began the laborious process.
Mr Kiir, now with a green-inked finger, presumably ignored the ballot box marked "Sudan presidential election", as his SPLM candidate, Yasir Arman, had earlier withdrawn from the race citing a rigged event.
We can also assume Mr Kiir's certain victory in the southern presidential race was kick-started with a vote for himself.
There were, however, reports that Mr Kiir accidentally posted at least one of the remaining ten ballots into the wrong box after officials failed to guide him through the process.
With presidential, parliamentary and local elections taking place, each voter in the south is making 12 decisions - it is a good job there are three days of voting ahead.
Reports from other parts of the south indicate that queues are building up as the temperatures start to creep up to the stifling 40C mark.
There are likely to be some heated races where candidates who were not nominated by Mr Kiir's Sudan People's Liberation Movement (SPLM) are standing as independents.
The event in the south is also complicated by the fact that insecurity over the past year displaced thousands.
In Akobo near the Ethiopian border, displaced people living in makeshift shelters proudly showed me their registration cards
The fact that some candidates have withdrawn does not necessarily mean they will not secure votes.
"I am voting for SPLM's Yasir Arman for president of Sudan," Elijah Garang told me at a cattle camp outside Juba.
"Even if he has withdrawn, he is my candidate and I will vote for him," said Garang who lost all five of his brothers in the north-south war.
It will be interesting to see how many others ignore the boycott.
MOHAMED KHALID, FASHER
The turnout in the North Darfur capital, Fasher, seems to be surprisingly high.
Several opposition parties refused to contest the poll in Darfur
At the al-Salam refugee camp, hundreds of people, mostly women, were queuing up to cast their ballots.
The start of polling was delayed by about an hour, however, because the election materials were not ready in many polling stations.
Security is tight, with two cars full of Sudanese soldiers waiting outside the voting centres.
"I came because I believe the election is very important for me and for Sudan," said Adam Isa, a middle-aged man.
"We want the election to bring change and peace and to help us go back home."
Elsewhere, the city is very quiet.
There have been no reports of any attacks in Darfur.
Although European Union election observers have left Darfur citing security fears, there are other observers here.
I have seen teams from the Arab League, the African Union and the East African regional body, Igad.
Several opposition parties have withdrawn from the elections in Darfur, saying it is impossible to hold free and fair polls in a conflict zone.