NATO and Russia have agreed to begin immediate talks on a European missile defence shield - something that had been a barrier to closer ties.
The BBC reports that the project was first put forward by Washington and has long caused friction.
The announcement was made by NATO secretary-general, Anders Fogh Rasmussen, at a NATO summit in Portugal, which he hailed as a turning point in the history of the alliance.
Russian president Dmitry Medvedev says there has been successful cooperation.
This is the first NATO summit Russia had attended since the Russia-Georgia war two years ago.
Nato members had earlier agreed on a programme to develop and deploy defences against ballistic missile attack on their territories.
Mr Rasmussen said he had extended an offer to Russia to co-operate on the programme and was "very pleased that [Russian President Dmitry] Medvedev has taken up that offer".
