Hundreds of legislators from all 28 member states will converge on the Scottish capital for discussions on a range of security matters.
Non-member countries - including Korea, Pakistan, Afghanistan and Russia - will also be present.
British Foreign Secretary David Miliband is due to address the 55th annual assembly, hosted by the UK Government, when it closes on Tuesday.
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The Nato assembly will focus on six themes before drawing up resolutions.
These will include reinforcing nuclear non-proliferation and "moving beyond" the economic crisis.
Today's opening session will be addressed by assembly president John Tanner and Bruce George MP, leader of the UK delegation. Committees are scheduled for Saturday.
Protests are expected over the weekend, including a rally organised by the "Nato Welcoming Committee".
A mass demo is being called to coincide with the first day of the assembly, and other "target" firms, linked to Nato, have been posted on protest websites.
Flyers have appeared around the city calling on people to "crash their party".
A separate event today at the Scottish Parliament has been organised by SNP MSP Bill Kidd as a "counterpoint" to the Nato assembly.
The backbencher said: "It is my intention to reiterate the commitment of the Scottish Parliament, the Scottish Government and the Scottish National Party to nuclear non-proliferation and disarmament."