Delegates from nearly 190 countries are meeting for two weeks in Bali to discuss climate change.
A principal objective is to agree a "Bali roadmap", a process leading to a successor agreement to the Kyoto Protocol, whose targets for reducing greenhouse gas emissions expire in 2012.
Where do the talks fit into wider moves to curb global warming? What are the main issues on the table?
What are the talks officially about?
The two-week meeting is officially described as the Thirteenth Conference of the Parties to the UN Framework Convention on Climate Change (UNFCCC) and the Third Meeting of the Parties to the Kyoto Protocol.
In plain language, that makes it the thirteenth summit of countries signed up to the UN convention, which dates from the Rio de Janeiro Earth Summit of 1992, and the third meeting of countries inside the Kyoto Protocol since that came into force in February 2005.
The UN convention commits the global community to "avoiding dangerous climate change", while the protocol sets binding targets on greenhouse gas emissions for industrialised nations.
Why is a Kyoto successor needed?
The protocol was only ever envisaged as a first step towards bigger emission cuts. Its current targets expire in 2012, and without a successor there will be nothing committing any country to reduce emissions beyond that date.
The protocol asked developed countries to cut carbon emissions by an average of about 5% from 1990 levels by the period 2008-2012.
For a variety of reasons, the actual cuts produced by 2012 will be much smaller. Many Kyoto countries are set to miss their targets by a long way.
The latest scientific assessment from the Intergovernmental Panel on Climate Change (IPCC) have added urgency to the quest for deeper cuts.
Its scientists recommend that globally, emissions should peak and start to fall within 10-15 years, sooner if possible.
Who is asking for what in Bali?
The European Union is heading efforts to secure a new set of targets that would reduce emissions from developed nations by 25-40% by 2020.
It would also like the more advanced developing nations to take on firmer commitments than they have at present, possibly also including concrete targets, though smaller than those facing richer countries.
Many countries, richer and poorer, including the US, Canada and India, are not prepared to accept binding numerical emissions targets at this stage.
How urgent is the need for an agreement in Bali?
A widespread consensus holds that a new set of targets should be in place by the end of 2009 - just two years away.
That would give governments and businesses enough time to put the necessary measures in place before 2012.
New targets would translate into a new set of parameters for the global carbon market, which businesses would need in order to plan for a carbon-constrained future.
What else has been on the table?
Three other big issues have been adaptation, forests and technology.
Poorer nations want money to protect themselves against the impacts of climate change, such as rising seas, drought, and reduced crop yields.
They say western countries' prosperity has developed on the back of high-emission economies, and should pay for the effects of the pollution they have produced.
They want the west to provide clean technologies in areas such as renewable energy.
Countries with abundant forests, including the meeting host Indonesia, want developed nations to pay for protecting their trees.
In principle, many western governments agree with all three ideas.
But differences remain on how best to provide the money, how much is needed, and how to oversee spending.
Some western delegates believe the developing world should sign on to the principle of reducing its emissions in exchange for more adaptation money.
What is happening outside the UN process?
There is a plethora of other climate initiatives - the US-led "big emitters" process, the G8, and the Asia-Pacific Partnership for Clean Development and Climate, to name but three.
Many environmental campaigners regard these as distracting side-shows that cannot promise real emission cuts.
The recent Asia-Pacific Economic Co-operation (Apec) forum in Sydney saw more than 20 nations agree to voluntary targets on improving "energy intensity" - the ratio of GDP to energy use - but these targets, even if implemented, could lead to a rise in carbon emissions.
None of these other initatives contain measures comparable to those in the Kyoto Protocol for adaptation, reforestation, and technology transfer.
Most developing countries, and the EU, are adamant that the UN process should remain paramount; and it is the only process that includes virtually all of the world's nations.
What happens next?
The UN climate roadshow moves on, with or without its roadmap, to Poland in December 2008 and Denmark in 2009.
If Bali is succesful, the second of those meetings should see the finalising of a Kyoto successor treaty.