By Damian Grammaticas
BBC Moscow correspondent
Russian President Vladimir Putin has arrived in China for an official visit which will aim to promote growing co-operation between the two countries.
Mr Putin's Russia has vast resources which China desperately needs
Russia and China are forging closer energy, trade and military links.
They also have similar diplomatic positions on sensitive issues such as Iran's nuclear programme.
Mr Putin and China's Hu Jintao may want to co-ordinate their opposition to Western calls for tough action against Iran by the UN Security Council.
On his last state visit to China, Mr Putin paid homage to its ancient terracotta warriors.
It was an apt symbol - old rivalries being replaced by a new, modern pragmatism.
Today, where Moscow and Beijing see their interests intersect they are co-operating as never before.
Following decades of mutual hostility that is a huge change.
Russia and China may want to repeat joint military exercises
Both are keen to reassert themselves as resurgent powers, alternatives to US dominance in international affairs.
But above all there is a logic to co-operation.
Russia has vast resources, China has a hungry, booming economy.
First and foremost it is energy China needs - and Russia has huge deposits just across the border in Siberia.
This time the two leaders will discuss plans for new oil and gas pipelines, more coal and electricity supplies and greater co-operation over nuclear power.
Last year Russia and China held their first ever joint military exercises. They are looking to repeat those this year.
And on international issues like Iran's nuclear programme, the two presidents may seek to co-ordinate their opposition to the line being taken by the US, Britain and France.
Western nations are pressing for tough action by the United Nations Security Council.
Beijing and Moscow, which wield UN vetoes, both want more time for negotiations with Iran, fearing that ultimatums and sanctions will only make the dispute harder to resolve.