IOs are groups which have been chartered by the NSS to further promote the purposes of the NSS. The privileges and responsibilities of IOs, as well as the criteria by which they are chartered, are set forth in the Policy for Internal Organizations as approved by the Board of Governors. Executive committee members of an IO must be NSS members.

A Grotto is an Internal Organization made up of individuals who reside in the same general locality or who cave together and maintain community by means of electronic or other communications. A Grotto must have at least five NSS members who have designated the grotto as their Primary Affiliation.

A Region is an Internal Organization made up of individuals and organizations in a general geographic area. A Region must have at least two other IOs who are members of the Region.

A Survey is an Internal Organization made up of individuals and organizations engaged in gathering speleological data in a general geographic area. 

A Section is an Internal Organization made up of individuals involved in a common study or interest related to speleology. A Section must have at least ten NSS members who are members of the Section.

An Affinity Group is an organization which will foster the NSS goal of fellowship among those interested in caves with common interests of their members not directly related to speleology. An Affinity Group is not an Internal Organization and does not have the privileges and obligations of an Internal Organization. The purpose of an affinity group must be compatible with the purposes and policies of the NSS. An Affinity Group must have at least ten NSS members who are members of the Affinity Group.