By Jill McGivering
BBC Asia analyst
India and China are obvious and formidable twins.
Cities like Shanghai point to a prosperous future
With a combined population of almost two-and-a-half billion people, they are the emerging giants of the new century.
Both are seeing dramatic levels of economic growth.
Both are increasingly dynamic members of the international community, increasingly conscious of their growing influence and feted by Western governments.
The central governments in both countries have found a new pragmatism in international affairs, eager to forge strategic relationships based on fuelling their growing energy needs at home.
China has built an impressive new network of political relationships with countries rich in resources - whether in Latin America and Africa or closer to home.
India, chasing many of the same resources, is racing to keep up.
Finding a new place on the world stage, marrying pragmatism and self-interest with the urging of countries like the United States to be responsible and altruistic global citizens, is difficult enough.
But the greatest challenge for both countries is managing the threat within - the threat of social instability which is increasingly preoccupying them both.
Again, there are obvious parallels.
China and India are both vast and diverse territories which pull together disparate cultures, ethnic groups and identities.
Globalisation has brought a new openness which also means more outside influence.
Poverty is often only a few streets away from great wealth
Both governments are eager to maintain their territorial integrity - part of which means keeping a sense of nationhood and common identity at a time of dilution.
Both are seeing social discontent.
Mass migration to the thriving cities, as migrants seek out new opportunities, is creating acute urban social problems - from a lack of adequate housing to inadequate health care and education.
The clear gaps between the haves and have nots increase concern about urban crime.
The growth of the cities, intense economic activity and rising car ownership in both countries is causing massive problems of air and water pollution which both governments are now struggling to address.
By contrast, rural populations are increasingly frustrated, aware of the boom elsewhere but feeling hopelessly excluded from the new wealth.
Without education, many born into villages have little opportunity of finding a useful place for themselves in the new economy.
In both China and India, some less accessible rural areas are increasingly denuded, maintained by the old and very young as the able-bodied workers head for the cities.
Both governments are engaged in massive social programmes to stop rural discontent and help the excluded regions to join the economic party.
But given the size of their populations and the political need to keep overall growth levels high, alleviating discontent in the short term seems an almost impossible task.
One of the greatest questions is how these two giants will manage the relationship with each other
In India, programmes like the newly launched National Rural Employment Guarantee Scheme actually pay people to stay in rural areas and support them through periods of unemployment there.
Some applaud it as a bold attempt at rural regeneration.
Others say it doesn't lift rural communities out of poverty, just tries to stem an inevitable tide of rural-urban migration.
In China, migration, although much freer than before, is still regulated and constrained.
Rural protests are growing with alarming speed, many focused on the requisition of land for non-agricultural use and local corruption.
But just as both vast countries share many of the same problems, their different political systems make them very different animals.
India's democracy brings constraints but may ultimately deliver greater stability.
It's hard for the central government in Delhi to engage in long-term planning.
Democracy involves complicated deals with coalition partners and regular and unpredictable changes in leadership.
A strong civil society also means that any radical solutions to national problems, such as the need for energy or tackling pollution, often face a storm of opposition from one vocal quarter or another.
Will the strategic partnership turn into genuine friendship?
There's also a pressing need to maintain public confidence in the democratic process in the country's most poor and poorly governed states to counter civil unrest.
But India does benefit from a thriving non-government sector, a strong and outspoken media which helps to keep politicians accountable and highlight problems and, at the centre of it all, a relatively strong and independent legal system.
In China, the economic change has so far failed to bring these sorts of freedoms.
Some analysts say discontent is generally focussed at a local level.
Attitudes towards Beijing and the Chinese Communist Party as a national government are still largely approving.
But as Chinese society changes, its middle-class grows and outside influences increase, the CCP may not be able to take its monopoly on political power for granted.
One of the greatest questions is how these two giants will manage the relationship with each other.
Recently they forged a new strategic partnership - moving on from old disputes about ideology and boundaries with promises to work together.
They're certainly eager to learn from each other.
India wants to imitate China's low-cost manufacturing success.
China wants to follow India in developing global IT, hi-tech and service industries.
But how far is this a genuine friendship - and how far are the lingering differences, rivalries and suspicions just being submerged?
The coming decades are sure to be interesting times.