While much of Indian politics revolves around the two biggest national parties and their allies, there are other significant parties with a major presence in parliament.
Click on the links below to read about them.
LEFTIST AND COMMUNIST PARTIES
Leftist and communist parties are a significant force in Indian politics.
In these elections they recorded their best ever performance, collectively winning 61 seats. The Communist Party of India (Marxist) is the third largest single party in the house with 43 seats.
The other principal parties on the left are the Communist Party of India (CPI), the All India Forward Bloc and the Revolutionary Socialist Party.
The left's key strongholds are the southern state of Kerala and the eastern state of West Bengal.
They also have a presence in Andhra Pradesh, Bihar, Tamil Nadu and Tripura.
Although the left's power base in West Bengal has eroded somewhat in recent times following a successful challenge posed by the BJP and its regional ally, the Trinamool Congress, they are still a formidable force in that state.
Their strength in Kerala and West Bengal is ascribed to their success in implanting land reform policies through which large farm holdings were broken up and distributed among the poor.
The CPI was the first communist party to formally join an Indian federal government, when they were part of the government of Prime Minister Deve Gowda in 1996.
A move to make veteran communist leader Jyoti Basu prime minister at the time came unstuck when his party, the CPI(M), rejected the move.
Although the communist parties have traditionally been opponents of Congress, they have identified the Hindu-nationalist BJP as their key political enemy and are therefor backing the Congress-led coalition government.
The Samajwadi Party has a strong presence in Uttar Pradesh, India's most populous and politically influential state.
Its support base is made up of lower-caste Hindus and Muslims.
Once a part of the Janata Dal which formed a national government in 1989, the Samajwadi party broke away in 1992 to form a separate entity under the leadership of Mulayam Singh Yadav.
It won 36 parliamentary seats in these elections - its best performance ever - and is firmly established as a powerful regional party.
Mr Yadav heads the state government with the backing of the Congress and is backing it at the federal level.
An experienced politician who cut his teeth in the socialist politics of the 1970s, Mr Yadav has recently built strong ties with Indian industry and other power brokers.
But Mr Yadav's dream of making the Samajwadi Party a major player in national politics has suffered a setback since the Congress alliance does not really need his support.
BAHUJAN SAMAJ PARTY
The Bahujan Samaj Party (BSP), which promotes the rights of Dalits - low caste-Hindus formerly known as untouchables - has had an astonishing political rise since its inception in 1984.
It won 19 parliamentary seats, all in Uttar Pradesh where it is the Samajwadi Party's regional rival with a political base among Dalits and Muslims.
And there are signs that the party is gaining support elsewhere, particularly in Maharashtra where it cut into many votes of the Congress Party.
Headed by the outspoken Mayawati, the BSP has been voted into power in Uttar Pradesh state three times.
Tthe party has a considerable presence in Punjab as well as the central Indian state of Madhya Pradesh.
At the moment it is supporting the Congress-led national coalition, but it aims at becoming an influential national player.