The world's largest exercise in democracy, India's general election, will take weeks to complete and involve hundreds of millions of voters. BBC News explains the process.
When is the vote and who is involved?
People walk past shop selling political party flags
For logistical reasons, polling to elect a new Lok Sabha (lower house) will be staggered over five dates: 16 April, 23 April, 30 April, 7 May and 13 May.
Voting in some states will take place over several stages.
Counting is due on 16 May.
Some 714 million voters are eligible to cast ballots, with almost four million officials taking part.
How is the vote organised?
The Election Commission had to negotiate a long list of potential obstacles when scheduling the poll: it took school exams, holidays, festivals, the harvest and even the monsoon into account.
INDIAN ELECTION AT A GLANCE
Eligible voters: 714 million
Polling centres: 828,804
Voting days: 16, 23, 30 April; 7, 13 May
Vote counting: 16 May
Leading candidates: Manmohan Singh (Congress), LK Advani (BJP), Mayawati ("Third front")
The organisational challenge of the polling is huge. There are 828,804 polling centres, including one in Gujarat's Gir lion sanctuary for a single voter.
Many new centres have been set up to reduce the time voters have to travel, often across hills and rivers.
There will be extensive security measures in the state of Jammu and Kashmir, where separatist militants have been operating for almost two decades.
Electronic vote counting, introduced in 2004, will be used for a second time.
Photo electoral rolls will be used for the first time on a national level to help voter identification and help prevent fraud.
Many Indians are illiterate, and identify parties by their symbols.
Who is competing?
There are two main coalitions competing for power: the United Progressive Alliance (UPA), which has been in government for the past five years, and the opposition National Democratic Alliance (NDA).
The UPA is led by the Congress party, which dominated Indian politics for a long time before a decline, while the NDA is led by the Hindu nationalist Bharatiya Janata Party (BJP).
But the main parties are coming under pressure from an alliance of left-wing and regional parties who have united to form a "third front". It could coalesce around the Dalit chief minister of Uttar Pradesh, Mayawati.
What are the issues?
Voters will be casting judgement on Congress's policies over the past five years, including a $2.2bn (£1.6bn) rural employment guarantee programme, arguably the world's biggest such scheme, and a landmark right to information law.
Electronic vote counting will be used for the second time
Congress will point to rapid economic growth during its tenure and its investment in social policies and the country's power infrastructure. But growth has been hit over the past year, with job losses and rising costs likely to weigh on voters' minds.
The BJP/NDA has focused on India's internal security situation in the aftermath of the November 2008 Mumbai (Bombay) attacks, claiming the government has been ineffectual in cracking down on terrorism.
The opposition has also criticised Congress for what it says are slow and ham-handed economic reforms, while claiming that Prime Minister Manmohan Singh is ineffectual and under the thumb of Congress head Sonia Gandhi.
What are the possible outcomes?
The increasing fragmentation of Indian politics and rising power of regional parties has caused problems for both the Congress- and BJP-led coalitions.
Neither has been looking especially strong in the run up to the elections, observers say, and both have been scrambling to bolster their positions through regional alliances.
If the two main coalitions fail to win a clear majority, regional and leftist parties could play a crucial role. The third front could try to form a government itself.
Large scale boundary changes since the last elections contribute to the difficulty of predicting the outcome.
Will the vote be free and fair?
India has a long track record in organising peaceful and orderly elections on a massive scale.
Voter intimidation and vote buying have decreased dramatically in the past decade.
The build-up to this year's poll has also been marked by a row at the Election Commission, where election chief N Gopalaswami accused his colleague Navin Chawla of pro-Congress "bias" and recommended his removal.
Mr Chawla has denied the charge and refused to quit.