By Adam Easton
BBC News, Warsaw
Poland and the US will shortly begin formal negotiations on Washington's proposal to locate part of its missile defence shield on Polish soil.
The US defence secretary has been paving the way for deployment
The initial talks will last for two or three days, focusing on the legal aspects of basing US forces in Poland.
The US wants Poland to host 10 interceptor rockets capable of destroying long-range ballistic missiles fired from the Middle East.
Russia says the US plan would seriously destabilise global security.
The US also wants to site a radar system in the Czech Republic.
Broader political discussions with Poland will take place at the end of the month.
The Polish government has said it wants to host the US base given the right conditions, despite growing public opposition.
Poland is a staunch US ally but it does not want to be taken for granted.
Polish officials were annoyed when the Americans sent their first official note on the base with a draft reply already attached. The government says any agreement must improve national security.
Ideally, the Poles want a new formal security partnership with the Americans and perhaps the deployment of batteries of short-range missiles.
Warsaw is well aware the shield may worsen its already frosty relations with Russia.