Voting in the Indian election takes place in five phases from 16 April - 13 May. The result is announced on Saturday 16 May. Click on the buttons below to see the phases of voting.
Seats: 80 Population: 166 million
Once a Congress Party stronghold, India's most populous state is now dominated by two caste-based parties, the Bahujan Samaj Party (BSP) led by Dalit (formerly untouchable) leader Mayawati, and the Samajwadi Party (SP) of Mulayam Singh Yadav, which draws support from lower castes and Muslims. The two parties won 54 seats between them in 2004, while Congress and the BJP won 19 between them.
Acute poverty, rising crime, poor infrastructure and abysmal healthcare are the biggest problems in the state, often referred to as India's Hindi heartland.
Mayawati's BSP is looking to repeat its sweeping victory in 2007 state elections. It has assiduously cultivated upper-caste Hindus to refashion itself as a rainbow coalition of high and low castes.
Mayawati has ambitions to become a pan-Indian leader and could be a crucial player in coalition negotiations once the votes are counted. It is even possible she could emerge as prime minister at the head of a Third Front of communist and left-wing parties.
Bihar is renowned as one of India's poorest and most lawless states.
Two regional parties - the Rashtriya Janata Dal (RJD) and the Janata Dal United (JDU) - dominate the political landscape. Both have links with the country's main political parties, the RJD with Congress, and the JDU with the BJP.
In 2004, the RJD, led by the flamboyant Laloo Yadav, picked up more than half of the state's seats, while the JDU managed only six. Mr Yadav went on to become railway minister in the Congress-led government. He has been credited with turning around India's ailing train network.
But the tables have turned since 2004. The JDU and BJP swept state polls in 2005, with JDU leader Nitish Kumar cashing in on popular disenchantment with the RJD government and the deteriorating law and order situation.
To make things worse for the Congress, its alliance with RJD has collapsed this time over distribution of seats. In a curious political twist, the RJD is now contesting the election in alliance with another UPA partner, Lok Janashakti Party (LJP).
So the main battle in Bihar this time is between the JDU-BJP alliance and RJD-LJP alliance. Deserted by its allies, Congress has been reduced to a small player.
Bihar needs to catch up with the rest of India - and jobs, development, infrastructure and security are what its voters demand.
One of India's most economically developed states - and one of its most politically volatile. Known as India's Detroit for its car making, it also has a strong services sector and a booming film industry.
The main contest will be between two of India's most powerful regional parties, the DMK and the AIADMK. Since the 1960s, regional parties have tapped into nascent Tamil nationalism and lower caste aspirations.
M Karunanidhi, an astute scriptwriter, heads the DMK, which governs the state. Pitted against him is a controversial former actress, the feisty J Jayalalitha, who leads the AIADMK. The dominance of these two personality-driven parties is so great that no national party has been able to make substantial political headway in Tamil Nadu in the last three decades.
In 2004 the DMK coalition swept every seat. But Tamil Nadu is considered a swing state. Whoever wins there is likely to play an important role in the forming of India's new coalition government.
Andhra Pradesh is marked by extreme affluence - there are vast farms and a burgeoning info-tech and services industry - and desperate poverty. The state also faces a separatist movement in the poverty-ridden Telangana region.
State and federal elections are both taking place here, with a keen contest in prospect between the ruling Congress Party and the main opposition alliance, led by the Telugu Desam Party (TDP) with the support of the communists.
Andhra Pradesh was a Congress stronghold until the TDP emerged in the 1980s. In 2004, a Congress-led alliance swept the polls, winning 37 seats. Five years earlier an alliance between the TDP and the BJP had taken 36.
Congress is banking this time on schemes like cheap rice, free electricity for farmers, free health cover for poor families and cheap loans for women.
Meanwhile, Chandrababu Naidu, the TDP leader hailed in the West as a mascot of economic reforms, is promising free electricity and television sets and unemployment benefit.
State and general elections are both likely to be three-sided contests, following a split in March between the Biju Janata Dal (BJD) and the BJP - former allies who governed the state together.
Both will now fight each other as well as Congress, the main opposition in the state.
The BJD hopes to win voter support with recently introduced measures, including cheap rice for the poor, better pay for government employees and better pensions for the elderly.
Congress says it will focus its campaign on calls to eliminate corruption, which it says has escalated over the last nine years. The BJP says the deterioration of law and order will be one of its election priorities.
Analysts says the state could be heading for a hung assembly. Congress should in theory benefit from the BJD-BJP split, but it may not be able to emerge as a clear winner.
Orissa is no stranger to hung assemblies and has had them regularly since the 1950s.
After last November's attacks in Mumbai, security is a key issue in this state, which is home to India's financial capital.
The Congress Party's Vilasrao Deshmukh had to resign as chief minister in Maharashtra - along with deputy RR Patil - for perceived failures over the Mumbai attacks. It has formed a pre-poll alliance and seat-sharing pact with the Nationalist Congress Party of Sharad Pawar.
The head of the right-wing Hindu Shiv Sena party, Bal Thackeray, has been ill and has made few public appearances. His nephew, Raj Thackeray, meanwhile, has formed a new party, the Maharashtra Navnirmaan Sena, along similar right-wing nationalist lines but is unlikely to make a big impact at national level.
The BJP is likely to focus on security, and the suicide rate among farmers suffering financial difficulties.
A critical shortage of electricity - with cuts ranging from four to 16 hours a day in most parts of the state - is also among voters' major concerns.
A left-wing coalition has governed the state for more than three decades. The left won 35 parliamentary seats in West Bengal in the 2004 elections, with Congress winning six and the Trinamul Congress one.
But the opposition parties are upbeat about how they will perform this time and are expecting to make major gains.
But now it seems the left is in trouble. The once-loyal rural poor have turned against Chief Minister Buddhadev Bhattacharya, as he pushes ahead with his plans to acquire farmland for big industrial projects.
The opposition, especially the Trinamul Congress - a party specific to West Bengal - have joined protests against large-scale land acquisition.
But Mr Bhattacharya insists that West Bengal must rapidly industrialise in order to provide jobs for millions of unemployed men and women.
"The iron discipline of the left is wilting after three decades in power. This election will be a real wake-up call for them," says political analyst Sabyasachi Basu Ray Chaudhuri.
Congress campaigned hard in Gujarat's state elections in 2007, but still lost to the BJP, allowing the controversial Narendra Modi to become chief minister for the third time in a row.
Mr Modi won the 2002 election on a Hindu nationalist platform shortly after the massacre of some 1,000 Muslims in Gujarat. In 2007, he toned down his nationalist rhetoric and campaigned on his economic record - the state's economy has been growing roughly 10% per year, above the national average.
Mr Modi appointed a Muslim as the state's police chief in February, in what analysts see as an attempt to court a secular image. But the arrest and resignation of the state's education minister on 27 March, in connection with the 2002 riots, is seen as a major embarrassment for the party.
Mr Modi is considered a possible successor to the ageing BJP leader LK Advani and will be hitting the campaign trail in other parts of India.
A communist bastion with the highest literacy rates in India. Nearly a quarter of its population are Muslim. The Left Democratic Front (LDF) alliance won 19 of 20 parliamentary seats in 2004. The Congress-led alliance won just one.
Infighting within the Communist Party of India (Marxist), or CPI(M), is likely to mean the left does less well this time. Traditional CPI(M) allies are unhappy at Chief Minister VS Achuthanandan's links with Abdul Nasser Madani, who leads the People's Democratic Party (PDP).
Mr Madani was arrested in 1998 in connection with an election rally blast in Tamil Nadu in which 60 people were killed. He was acquitted of all charges in 2007, but some of the mud has stuck.
Strained ties with another former ally, the Janata Dal (Secular), are also expected to work against the CPI(M).
The Congress party has been making a major push in the state, sending Rahul Gandhi to campaign. It is also fielding former UN under secretary general Shashi Tharoor as a candidate.
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