A guide to India's main political parties and coalitions as they headed into the 15th general elections and how they are likely to fare.
No party is expected to win a clear majority
India's two main parties, Congress and the Bharatiya Janata Party (BJP), had 145 and 138 seats respectively in the outgoing 543-seater lower house of parliament.
In a replay of the last election, neither party is likely to form a government on its own.
A coalition of parties reflecting regional aspirations, caste kinships and sectarian divides, is likely to emerge as the winner.
Taking on the Congress-led United Progressive Alliance (UPA) and the BJP-led National Democratic Alliance (NDA) is the newly formed Third Front, a clutch of Left and regional parties.
Also, regional allies began deserting coalitions in the run up to the elections, leading to the possibility of realignments after the results were out.
The three main coalitions are:
UNITED PROGRESSIVE ALLIANCE
The Congress party-led UPA had the support of 263 MPs in the outgoing parliament. Of this, the Congress party had 145 MPs of its own.
India's Grand Old Party has not ruled out seeking alliances with parties which are presently not in the UPA after the elections are over.
The party's dwindling base in former strongholds like Uttar Pradesh, Maharashtra and Bihar, is a major cause of worry for its leaders.
In many of these states, the party has been forced to play second fiddle to its allies, who are powerful there. For example, the regional Rashtriya Janata Dal (RLD), a key ally of the UPA, is the dominant partner in Bihar state.
In 2004 elections the Congress-led UPA's biggest support came from the Left parties, led by the Communist Party of India (Marxist). The Left parties mopped up 59 seats and supported the government from outside.
But these parties withdrew support to the government over the landmark civilian nuclear deal with the US in 2008.
The Congress is India's oldest political party
They are now are a part of the Third Front, a disparate grouping of secular Left and regional parties.
The problem with the Congress is that some of its key allies have become so powerful in their regions that they refuse to let the party grow in strength there.
Two key Congress allies - the Samajwadi Party (SP) in Uttar Pradesh with 36 seats and RJD in Bihar with 24 seats - have refused to go in for "equitable" seat adjustments with the party.
As a result, Congress contested alone in Bihar and UP with bleak prospects.
In UP, the party's failure to stitch up an alliance with Samajwadi Party could end up helping the regional rival Bahujan Samaj Party's Mayawati, who is nursing prime ministerial ambitions.
Congress can be satisfied with seat adjustments with allies in only two states: the Trinamul Congress in West Bengal and the Nationalist Congress Party (NCP) in Maharashtra.
The UPA has an edge in the elections on the possibility of Congress doing well in Kerala, Andhra Pradesh, Rajasthan and West Bengal, and its major constituents like the SP, RJD, TMC, NCP retaining good numbers and then staying with the alliance.
NATIONAL DEMOCRATIC ALLIANCE
The Hindu nationalist Bharatiya Janata Party won 138 seats, just seven seats short of Congress's 145 seats in the last elections.
However, its major allies in the party-led National Democratic Alliance (NDA) have either parted company or are seriously considering the option.
Mr Advani is NDA's prime ministerial candidate
The Biju Janata Dal (BJD) in Orissa (11 seats) has already left the alliance. And the Janata Dal United (JDU) in Bihar (eight seats) is having second thoughts about staying within the alliance at the time of writing this.
The chances of the NDA improving its tally hinges on the party improving its strength in states like Gujarat, Madhya Pradesh, Jharkhand and Bihar.
Smaller allies like the Rashtriya Lok Dal (RLD) and Asom Gana Parishad (AGP) with five seats between them would hardly make a decisive difference even if their tally increased this time.
With the BJD gone and no new alliances formed, the BJP-led coalition appears to be in some trouble.
The prime movers of the Third Front are the Left parties, mainly the CPM (43 seats), CPI (10 seats) and the RSP and the Forward Bloc (three seats each).
The second biggest partner, the Bahujan Samaj Party (19 seats) has said it will lend its support to the Front as long as its leader Mayawati is the Front's prime ministerial favourite.
Others partners like the regional Telugu Desam Party and Telegana Rashrtiya Samity (five seats each) are expected to improve their tallies.
The regional AIADMK (12 seats) and the BJD (11 seats) parties are also some other key Third Front parties.
The Third Front could end up playing a decisive factor
The Third Front has become a shelter for any party which feels marginalised in the two main coalitions.
This rump coalition of parties cutting across ideology - communists and caste-based parties make strange bedfellows in the Third Front - could emerge as a decisive force if the Congress and BJP with their committed allies fall reasonably short of the simple majority figure of 272 seats to form a government.
Being a group of secular parties, they are likely to end up supporting a Congress-led government. And if the Congress tally drops drastically, they would pitch for leading a government, supported by the Congress.
The newest of India's myriad coalitions, the Fourth Front is nothing more than an opportunistic alliance which will not stand the test of election results, critics say.
But it nevertheless contains some key politicians including Mulayam Singh Yadav, the Samajwadi party leader in Uttar Pradesh and Lalu Prasad Yadav - who is also India's railway minister - of the Rashtriya Janata Dal party in the state of Bihar.
Analysts say the two politicians have got together to ensure that the Yadav vote - which is traditionally provided by millions of agricultural workers - is consolidated in the two states.
Both leaders also have a strong support base among Muslims, who form a strong voting bloc in UP and Bihar which accounts for 120 out of the 543 parliamentary seats.
Other key members of the Fourth Front include Ramvilas Paswan, expected to pick up many low caste votes and the Prarajyam Party of the Andhra Pradesh film star, Chiranjeevi.
Correspondents say that because the Fourth Front is a loosely formed alliance, it may well disintegrate once the votes are counted, depending on who offers them the best deal in terms of a stake in the new government.
These include Tamil Nadu-based parties such as the MDMK of Gopalswamy Vaiko, which takes a strident line on the Sri Lankan war. It is seen as close to Tamil Tiger leader Prabhakaran. Another Tamil party, the PMK, has strong support among the influential weaving community. Both the MDMK and the PMK supported the DMK of Chief Minister M Karunanidhi in the last elections, but this time have announced that they will support the AIADMK of his main rival Jayalalitha. One other party - the DMDK may also pick up votes as it is led by the charismatic film star, Vijaykant.
Among other parties who are not aligned with the four blocs are the left-of-centre Janata Dal (Secular) of former PM Deve Gowda, the Haryana Janahit Party and the Janhit Congress Party.
Vipul Mudgal of the Centre for the Study of Developing Societies assisted in the research this article.