More than 10 percent of the world's population is eligible to vote in India's election, the largest democratic exercise in history.
With India's population at 1.34 billion people there are more than 900 million eligible voters for this year's election - nearly four times as many as the next largest democracy, the United States.
The country has upper and lower houses of parliament known as Rajya Sabha and Lok Sabha respectively. Rajya Sabha is elected by state lawmakers and the President, while Lok Sabha - the house of the people - is elected by the voters: that's the one to watch.
The election for Lok Sabha will take place at different times in different states in seven stages between 11 April and 19 May, using a First Past the Post system. Votes will be tallied on 23 May.
It will decide if Hindu nationalist Prime Minister Narendra Modi will run the country for another five years. The election is being seen as a referendum on Mr Modi, and analysts are divided on whether he will be able to win a simple majority again.
He swept to power in 2014 with bold economic promises but his record in office has been mixed. Economic growth has hovered around 7 percent a year, and before long the Indian economy is likely to overtake the UK as the world's fifth-largest.
The number living of people in India below the international poverty line has decreased from 21.6 percent in 2011 to 13.4 percent, and some of Mr Modi's ambitious reforms - like a Goods and Services tax - have been praised.
However, unemployment is the highest it's been since 1973, and Mr Modi's sudden withdrawal of large-value banknotes in 2016 is seen as a failure.
Farmers promised doubled incomes by 2022 are angry over low crop prices and have been protesting, while Mr Modi has also been accused of stoking divisions between the Hindus - about 80 percent of the population - and the country's 200 million Muslims.
Mr Modi's main rival is opposition leader Rahul Gandhi, heir to the famous Gandhi-Nehru political dynasty. He has long been seen as aloof and a poor campaigner, but that image has been changing in recent times.
Mr Gandhi's Congress Party is part of a larger coalition of centre-left parties called the United Progressive Alliance (UPA), while Mr Modi's ruling Bharatiya Janata Party (BJP) is part of the centre-right National Democratic Alliance (NDA).
Any coalition would need a minimum of 272 MPs in the 543-seat Lok Sabha.
Mr Gandhi's Congress Party only took 44 seats in 2014, while Mr Modi and his BJP won 282 seats and were seen as the overwhelming favourites to win the election.
The party's loss of key states in December's regional elections - Chhattisgarh, Madhya Pradesh and Rajasthan, all part of India's Hindi-speaking heartland which helped Mr Modi win in 2014 - has however injected a sense of serious competition.
Meanwhile tensions with Pakistan - against which India has fought three wars since gaining independence in 1947 - have also been on the rise with each side carrying out air strikes. The conflict has given the nationalist BJP a new and popular issue to campaign on.