No party is expected to win enough seats to govern alone, which could mean months of political uncertainty as parties discuss forming a coalition government.
"No party will have a clear mandate in the upcoming elections," said MJ Akbar, a political commentator, noting that several coalitions have governed India since 1996.
The major parties have already begun unofficial campaigns, with Pakistan, violence, Hindu nationalism and the economic slowdown among the key issues.
Following the series of attacks in Mumbai in November, the government has raised defence spending by nearly one- quarter.
The election comes amid a sharp decline in the economy as domestic demand and exports slump.
But the government has also presided over a fall in inflation, while financial help to the farm sector and a jobs scheme have lifted millions of people in the countryside out of poverty.