NATO, or the North Atlantic Treaty Organisation, was formed in 1949 in an attempt to bind the non-communist states of Western Europe and North America together in the face of Soviet-backed expansion and aggression after the end of the Second World War.
Importantly, it was a way of uniting European states under the protection of US nuclear umbrella, which in 1949, no European states possessed.
Here is footage of Nato's founding meeting in Washington in 1949:
Nato's main principle is collective security - in other words, an attack on one state is viewed as an attack on all - and all member states must then come to the aid of the one who is under attack.
This principle in Article 5 of the founding North Atlantic Treaty has only been invoked once - in 2001 after the 9/11 attacks. This saw forces from Nato countries deployed in Afghanistan.
Since the fall of the Berlin Wall in 1989 and the end of the Cold War in 1991, Nato engaged in its first major crisis-management operation in Bosnia and Herzegovina in 1995. It then led operations in 1999 to prevent Yugoslavian incursions into Kosovo.
Following the 9/11 attacks Nato adopted a broader approach to security, involving counter-terrorism.
In 2003 NATO took command of the International Security Assistance Force - ISAF - in Afghanistan.
Other operations Nato have taken on include intervention in the Libyan civil war in 2011, combating piracy in the Gulf of Aden from 2009.
What is the Nato Summit for?
A NATO summit is a summit meeting that is regarded as a "periodic opportunity for Heads of State and Heads of Government of NATO member countries to evaluate and provide strategic direction for Alliance activities". The first summit was in Paris in 1957 and the last was in Chicago in 2012.
Delegates will discuss:
Crisis in Ukraine and relationship with Russia
Tackling new threats
Strengthening support for Armed Forces across Nato
The alliance was founded by 12 countries and now has 28 member states, the newest of which, Albania and Croatia, joined in April 2009.
60 countries will be represented at the Newport summit, although many of these are outside the alliance, like Algeria or Australia, are involved in partnerships covering different areas of the globe.
Member states and year they joined:
The United Kingdom
The United States