IIW members are associations or institutes representing the welding stakeholders of a country.

According to the Constitution of the IIW, members are:

• legally established in accordance with the laws and practices of their country,
• non-profit distributing organisations,
• organised and financed to take into consideration and/or to represent the interests of those industrial domains that make use of techniques within the technical field of the IIW,
• financially adequate for sharing the work of the IIW and representing the interests and objectives of the IIW in their country.

In some countries, IIW has more than one member society. In this case, one of them is appointed as Responsible Member Society and is responsible for representing the interests and objectives of their country in IIW.