The NATO-PA is made up of 257 delegates from the 28 NATO member countries. Each delegation is based on the country's size and reflects the political composition of the parliament, therefore representing a broad spectrum of political opinion. Delegates are nominated by their parliaments according to their national procedures.

In addition to NATO-country delegates, delegates from 14 associate countries, 4 Mediterranean associate countries, as well as observers from 7 other countries take part in its activities, bringing the total number of delegates to approximately 360.

Associate members are able to participate in almost all Committee and Sub-Committee activities, all Rose-Roth seminars, and Plenary Sessions. At Plenary Sessions, associate members can present resolutions and amendments to resolutions. They can also serve as Special Associate Rapporteurs on Committees to present their perspectives in NATO-PA reports. They are not, however, eligible to vote on reports, resolutions or Assembly leadership, nor do they contribute to the Assembly’s budget.

Inter-parliamentary assemblies such as the OSCE Parliamentary Assembly (OSCE PA) and the Parliamentary Assembly of the Council of Europe (PACE) also send delegations.

The European Parliament is entitled to send ten delegates to Assembly Sessions and can participate in most Committee and Sub-Committee activities.

Other parliamentary delegations are invited on anad hocbasis for certain meetings and activities; in the past, these have included in particular delegations fromAfghanistan,Pakistan, the Assembly of Kosovo, and the Parliamentary Assembly of theMediterranean.CyprusandMalta, as well as a number of parliaments from North Africa and the Middle East, are also invited to seminars of theMediterraneanand Middle East Special Group.