Voters will choose representatives for the Indian parliament, and in turn decide if Hindu nationalist Prime Minister Narendra Modi will run the country for another five years.What is at stake?
Whoever wins these elections and forms a government will control the destiny of the world's largest democracy.
While they are in charge, India’s economy is likely to overtake the UK’s and become the world’s fifth-largest.
Its population meanwhile - at more than 1.34bn people - is predicted to soon surpass China’s 1.39bn.
Hundreds of millions of Indians have escaped poverty since the turn of the millennium but huge challenges remain.
Unemployment is a major concern and is especially high among young people.Millions of farmers are angry about low crop prices.
How the nuclear-armed country engages with the outside world – and manages a tricky relationship with its neighbour Pakistan – is also of immense importance to international security.
Who is being elected?
Indians are voting for members of parliament and the job of prime minister tends to go to the leader of the party or coalition with most seats. The current PM is Narendra Modi.
His main rival is opposition leader Rahul Gandhi.
Parliament has two houses: the Lok Sabha and the Rajya Sabha.
The lower house – Lok Sabha – is the one to watch.
It has 543 elected seats and any party or coalition needs a minimum of 272 MPs to form a government.
At the last election in 2014, Mr Modi’s BJP won 282 seats.
Mr Gandhi’s Congress Party only took 44 seats in 2014 – down from 206 in 2009.
Why does voting take so long?
Because of the enormous number of election officials and security personnel involved, voting will take place in seven stages between 11 April and 19 May.
Different states will vote at different times.
Votes will be counted on 23 May and results are expected on the same day.
Who will win?
This election is being seen as a referendum on Mr Modi, a polarising figure adored by many but also accused of stoking divisions between India’s Hindu majority and the country’s 200 million Muslims.
Until a few months ago, Mr Modi and his BJP party were seen as the overwhelming favourites. But the loss of key states in December’s regional elections injected a sense of serious competition into the national vote.
Analysts are divided on whether Mr Modi will be able to win a simple majority again.
A recent escalation of tensions with Pakistan has given the BJP a new and popular issue to campaign on.
It will be hoping that a focus on patriotism will help the party to get past the serious challenge mounted by powerful regional parties and Congress.