Joint Warrior is held twice a year - in spring and autumn.
The first of this year's exercises runs to 6 April and involves warships operating from Faslane on the Clyde and aircraft from RAF Lossiemouth, Moray.
Live firing training will also be held at a Ministry of Defence range at Cape Wrath in Sutherland.
Thirty-five naval units and more than 50 aircraft will be used during Joint Warrior.
Countries taking part include Denmark, Belgium, Estonia, France, Germany, the Netherlands, Norway, Spain, Sweden, the UK and the US.
About 430 of the thousands of personnel involved are co-ordinating the exercise from HM Naval Base Clyde's Maritime Operations Centre.
In the land based training, 16 Air Assault Brigade Headquarters and its associated battle group, 2 Para, have been joined by troops from the Netherlands, Sweden and the US.
This year's spring staging of Joint Warrior also involves the Royal Navy's first large scale cyber war games.
Information Warrior 17 will involve Artificial Intelligence (AI) and test the protection of warships and submarines against cyber attacks.
Thirty-five naval units and more than 50 aircraft will be used during Joint Warrior.
Thousands of Nato army, navy and air force personnel are in Scotland for one of the largest military exercises in Europe.