The Indian Election Commission has fixed the dates for the general election due this year.
Voting will take place between 16 April and 13 May.
Up to 714m people will be eligible to vote.
The chief of the Election Commission said counting of ballots will take place on 16 May.
The election comes just a few months after the Mumbai attacks and at a time when stability in neighbouring countries like Pakistan, Bangladesh and Sri Lanka is declining.
The main battle will be between the Congress-led coalition and the leading opposition bloc, headed by the Hindu-nationalist Bharatiya Janata Party (BJP).
Chief Election Commissioner N Gopalaswami told reporters voting would be held in five phases.
'The process of finalising the election schedule takes into account the school examinations ... the local holidays ... festivals, the harvest season and so on,' he said.
The staggered voting is to allow security forces to move around the country to curb any attempt to coerce the huge electorate.
Analysts so far see no party emerging with a clear majority from the election, which could mean weeks or even months of political uncertainty as parties negotiate for power.
If the alliances headed by the national parties - the Congress and BJP - fail to win power, pollsters and analysts say, a loose coalition of smaller parties known as the Third Front could come to office.
Chief among these are the communists, who thwarted pro-reform policies while supporting the incumbent Congress-led coalition.
While the financial crisis and security are seen as national issues, many experts say the vote could be dominated by a myriad of caste and regional alliances and local issues.
Despite the global recession, India's economy continues to grow. However, its 7.1% increase for fiscal year 2008/09 is the slowest pace in six years as domestic demand slumps and exports dip sharply.
It is still unclear how the slowdown will play out with the majority voters in the countryside where government financial help to the farm sector and a landmark jobs scheme have lifted millions out of poverty. Inflation has also fallen.
Analysts say the Congress has been able to checkmate opposition criticism over poor security after the Mumbai attacks by introducing a new terror law, improving security, changing the country's home minister and raising defence spending by nearly a quarter this year.
But another militant strike before the election could put terrorism on the top of the voter agenda.
India Election Scenarios
Here are the three most likely outcomes of the election which will determine who will head the next government, according to pollsters and political analysts.
Congress-led alliance
The incumbent United Progressive Alliance (UPA) led by the Congress party wins the biggest number of seats. It may also have to rely on support outside the coalition, such as the communist parties that propped up the government from 2004 to 2008.
This time, its former leftist allies, who quit the coalition over a civilian nuclear deal with the United States, may be hesitant about joining the government once again.
This means smaller regional parties, like the Dalit-based Bahujan Samaj Party (BSP) led by the controversial Mayawati, could become power brokers.
BJP-led alliance
The National Democratic Alliance, led by the Hindu-nationalist BJP, wins the biggest number of votes. Again, it could have more than 50% of seats or be dependent on a tie up with a regional party.
Third Front
If the UPA and the NDA fail to cobble together a coalition - or between them win less than half the total number of parliamentary seats - then a loose alliance of smaller parties could win power.
In India, these parties are known as the Third Front.
Chief among them are the communists, who thwarted several pro-reform policies of the UPA and pulled support over the nuclear deal. They have strongholds in three Indian states where they usually win enough seats to hold the balance of power in a hung parliament.
The Mayawati-led BSP or the Samajwadi Party, based in populous Uttar Pradesh state, could also play a major role in this government. The parties would choose a prime minister after post-poll negotiations.
