60 world leaders will spend the next two days discussing major security threats.
Russia has already come under criticism from Western leaders over its "destabilising" influence on the crisis in Ukraine.
UK priorities
1. Crisis in Ukraine and our relationship with Russia
2. Afghanistan's future
3. Tackling new threats
4. Strengthening support for our Armed Forces
5. Strengthening partnerships
Christian Tory MP John Glenn is calling for changes to the system to make sure NATO remains effective.
He said: "NATO is needing reform. Article 5 suggests if one of the members is attacked then they have a right to be defended by the other members and that's not efficiently working.
"Like the EU it's grown out of proportion to its original size and therefore maintaining those same obligations to the same level of seriousness has been very difficult to achieve."
With the last of the British troops set to leave Afghanistan in December, the leaders will discuss how to make sure peace remains in the country.
Christian DUP MP Jim Shannon is concerned it could end up being another Iraq.
He said: "We trained the Iraqi Army, we gave them the best equipment that anyone could give them. Americans and the British trained them personally and at the first sign of trouble they melted like the snow in the ditch.
"When it comes to Afghanistan, I want to be absolutely assured that the Afghan army not only have the training and equipment but they have the willpower, the commitment and enthusiasm to stand up to whatever comes."
The summit will come to a close tomorrow afternoon.
Listen to Christian MPs John Glenn and Jim Shannon here: