In a process will run for another month, voting begins today in India, the world’s largest democracy. Seventeen states go to the polls today; the rest vote progressively over the next three Thursdays and Wednesday 13 May. (The BBC has a handy map and guide.) There are 828,804 polling stations for the estimated 714 million eligible voters.

Prime Minister Manmohan Singh is leader of the Congress Party, which won a narrow surprise victory at the last election in 2004. Congress used to be unassailable, governing India for the first 30 years of independence, but has been in steady decline since then. A recent opinion poll put Congress and its allies in the lead but well short of an overall majority.

The only party to have formed a stable government without Congress was the Bharatiya Janata Party, in power from 1998 to 2004, which is now the main opposition. But smaller and regional parties have been gaining ground and it will be difficult for either side to put together a majority government: Congress and the BJP only had about half the vote between them last time and that proportion is expected to decline.

Ideologically, the BJP represents Hindu nationalism, whereas Congress represents the country’s more left-wing secular traditions. In practice both have governed from the centre. Both have pursued economic liberalisation; Singh is widely credited with starting the process as finance minister in a Congress government in the early 1990s, but the BJP continued a program of deregulation and privatisation.

Predicting a winner is made more difficult by the fact that votes do not reliably translate into seats. The 535 members of the lower house are elected from single-member constituencies, by first-past-the-post voting. That tends to advantage larger parties and those whose support is regionally concentrated, but because India is so large and so diverse the unfairnesses even out rather better than in most such systems. (Adam Carr has a fine set of electoral maps.)

Whoever ends up forming government will have a difficult task ahead.

Like many multi-ethnic countries, India seems to be getting harder to govern; terrorism is a continuing threat and the global financial crisis has taken its toll there as elsewhere. No-one rates highly the chance of a new government serving out a full term.

But India’s sense of a common history and national identity is still strong and its political class is used to working out differences peacefully, if sometimes inefficiently.

Most notably, India is a standing reproach to those who say that democracy can’t work in [insert favourite dictatorship here] due to its great size, complexity, poverty, troubled history, ethnic diversity or religious tension. Indian democracy starts with just about every disadvantage imaginable; it’s not surprising that it doesn’t always work well. But it does work.