Here are 10 facts on the Tamil Nadu polls:
This is first election after the death of the towering personalities of Tamil Nadu politics, DMK patriarch M Karunanidhi and AIADMK chief J Jayalalithaa.
The polls will therefore test the leadership of Karunanidhi's son MK Stalin, who succeeded him as party president, and also that of Chief Minister Edapadi Palaniswami and deputy chief minister O Paneerselvam, who now run the government and the AIADMK.
Though there are many parties in the contest, Tamil Nadu's politics is largely two-party with the AIADMK-BJP alliance pitted against the DMK-Congress alliance.
This time, two other personalities who have established new parties, could play spoilers. One is TTV Dhinakaran, the nephew of Jayalalithaa's close friend VK Sasikala, who heads the rebel AMMK, and actor-politician Kamal Haasan, who has fielded candidates from his debutant MNM.
Along with election to 39 Lok Sabha seats, by-polls will also be held for 18 assembly segments on April 18 and four more assembly seats on May 29. The AIADMK has to win at least five assembly seats for a majority in the state assembly.
Even though Jayalalithaa had declared in 2014 that the AIADMK would contest alone in future, regardless of her friendship with Prime Minister Narendra Modi, the party has tied up with the BJP as part of an eight-party alliance. They fight 20 seats, the BJP five, S Ramadoss' PMK six and the DMDK four, among others.
MK Stalin's DMK is in alliance with the Congress as part of the nine-party Secular Progressive Alliance. The DMK too is fighting 20 seats and the Congress will fight in 10.
Even though the AIADMK and DMK are contesting 20 seats each, they face each other directly only in eight.
TTV Dhinakaran's AMMK (election symbol gift item) and Kamal Haasan's MNM (election symbol torch light) have put up candidates in all 39 Lok Sabha seats and the bypolls as well, hoping to make a dent in the vote share.
Both national parties are hoping their alliance in Tamil Nadu will give them some room to manoeuvre at the centre, when it comes to support for a coalition.