Outgoing President Mwai Kibaki, the candidates and civil society groups have all appealed for a peaceful poll after the disputed vote five years ago unleashed a wave of killing by rival tribes that lasted weeks and left more than 1,200 dead.
"I also make a passionate plea for all of us to vote peacefully. Indeed, peace is a cornerstone of our development," Kibaki, barred from seeking a third five-year term, told Kenyans in a televised address before polling day.
Yet, as in 2007, the race has come down to a high-stakes head-to-head between two candidates, Prime Minister Raila Odinga and Deputy Prime Minister Uhuru Kenyatta, and once again both will depend heavily on votes from loyalists of rival tribes.
Though well ahead of six other contenders, polls suggest neither may be able to command enough ballots for an outright victory in the first round, which could set the stage for a tense run-off tentatively set for April 11. A narrow first round victory for either could raise prospects for legal challenges.
Kenya's neighbours are watching nervously, after their economies felt the shockwaves when violence five years ago shut down trade routes running through east Africa's biggest economy. Some landlocked states have stockpiled fuel and other materials.
The United States and other Western states are worried about the conduct of a poll in a state seen as a vital ally in the regional battle against militant Islam. Adding to election tensions, al Shabaab militants, battling Kenyan peacekeeping troops in Somalia, issued a veiled threat days before the vote.
But the West also frets about the result of the presidential race. One of the top candidates, Kenyatta, is indicted for crimes against humanity by the International Criminal Court.
"PEOPLE CAN DECIDE"
The 51-year-old, accused with his running mate William Ruto of instigating the post-2007 vote violence, denies the charges. But, if he wins, it would present a diplomatic dilemma for Western states who donate hundreds of millions dollars a year.
"There are those who said that Uhuru and Ruto will not run because we are facing cases in Europe, but God has opened that road for us so that people can decide," Kenyatta told a final rally in Nairobi's central park on Saturday, where thousands of supporters gathered, some chanting "Uhuru, Uhuru".
Like other candidates, he called on his supporters to vote peacefully and promised he would accept any result.
To try to prevent a repeat of the contested outcome that sparked violence after the December 2007 vote, a new, broadly respected election commission is using more technology to prevent fraud, speed up counting and increase transparency.
This could speed a result announcement, after delays in 2007 fuelled the crisis. Provisional figures may emerge within hours of polls closing, although the commission has seven days to declare the official outcome.
Police chiefs have deployed extra forces to maintain security and there is a more independent judiciary which commands greater respect. Officials have appealed to candidates to raise any challenges in the courts and not on the streets.
But Odinga has already raised a warning flag, telling Reuters that the commission had by "design or omission" not registered all voters in his strongholds, putting him at a disadvantage, a charge the commission denies.
"We know and we hope there will be no rigging this time," Odinga, who narrowly lost the 2007 race, told a Nairobi stadium filled with supporters.
"We are urging all our supporters to be peaceful because you are winning," said the 68-year-old, a veteran of Kenyan politics who may now have his last shot at the top job.
RUNNING DOWN STOCKS
Many Kenyans, hoping for a peaceful vote, say memories of the brutal killings by gangs armed with machetes, knives and bows and arrows are still fresh enough to deter a repeat.
Among crowds streaming from Kenyatta's rally, Pedro Sibinde, 34, declared his candidate would accept defeat if he lost. But, expecting a victory, he added: "I am confident (there will be peace) as long as our rival Mr Odinga concedes."
Yet others are more wary, particularly in places where violence flared last time. Shopkeepers have run down stocks and some people in mixed tribal areas have returned to their homelands elsewhere, a few worried by threatening leaflets.
Michael Ochieng, in the tense city of Kisumu on the shores of Lake Victoria where businesses were looted five years ago, said reports of such leaflets in Rift Valley areas, another site of slaughter after 2007, did not bode well.
He spoke of growing animosity between Odinga's Luo tribe and Kenyatta's Kikuyu, in a contest where many voters will make their decision based on tribal loyalties not ideology.
Alongside the presidential race, there are hotly contested elections for senators, county governors, members of parliament, women representatives in county assemblies and civic leaders.
In the teeming slum of Kibera in central Nairobi, where Luos and Kikuyus live side by side, the sight on the election's eve of orange t-shirts of Odinga supporters walking alongside the red ones of Kenyatta backers encouraged some.
But Samuel Kitai, 60, a grain miller who is neither Kikuyu nor Luo and whose store was looted in the 2007 violence, was taking no chances. Pointing inside his largely empty corrugated iron shack, he said: "I usually have maize here, rice and everything, but now you can see the store is empty."
(Additional reporting by Hezron Ochiel in Kisumu; Writing by Edmund Blair; Editing by Stephen Powell)