The Yearbook attempts to cover all “international organizations”, according to a broad range of criteria. It therefore includes many bodies that may be perceived as not being fully international, or as not being organizations as such. These bodies are nevertheless included so as to enable users to make their own evaluation in the light of their own criteria.

To assist this evaluation, the editors have developed two sets of codes referred to as Type I and Type II.

Type I

This hierarchical typology may be used to help determine the status or level of "internationality" of an organization.

Type A: Federations of international organizations
A principal membership category includes at least three autonomous international bodies
Type B: Universal membership organizations
Membership covers at least 60 countries regardless of distribution, or membership covers at least 30 countries and is equitably distributed over several continents
Type C: Intercontinental membership organizations
Membership exceeds that of a particular continental region, covers at least 10 countries, and is equitably distributed over at least two continents
Type D: Regionally defined membership organizations
Membership and preoccupations restricted to a particular continental or sub-continental region or contiguous group of countries, and covers at least 3 countries or includes at least 3 autonomous international bodies
Type E: Organizations emanating from places, persons or other bodies
May include international centres and institutes created by intergovernmental bodies, and joint bodies, regardless of membership
Type F: Organizations having a special form
May include foundations, funds, banks, and illegal or unusual bodies
Type G: Internationally-oriented national organizations
Includes bilateral bodies, organizations with membership or management structure limited to a single country yet name or activities indicate an international character, and national bodies with formal links (member, funder, partner) with a body of the UN system or other international organization
Type H: Inactive or dissolved international organizations
Dissolved or inactive organization previously classified as a Type A, B, C or D
Type J: Recently reported or proposed international organizations
Information available is insufficient to enable classification as another Type
Type K: Subsidiary and internal bodies
A substantive unit within a complex international organization which has a degree of autonomy
Type N: National organizations
Membership or management structure is essentially limited to a single country, yet title or activities make it appear to be international
Type R: Religious orders, fraternities and secular institutes
A religious or fraternal order or similar body based on commitment to a set of religious practices. Membership covers at least 3 countries
Type S: Autonomous conference series
Not an organization as such but represents a continuing series of international meetings which has a name which could be assumed to refer to an international body
Type T: Multilateral treaties and agreements
Not an organization as such but a multilateral treaty, convention, agreement, pact, protocol or covenant signed by at least 3 parties, whether States or intergovernmental organizations.
Type U: Inactive or dissolved non-conventional bodies
Dissolved or inactive organization previously classified as a Type other than A, B, C or D

Type II

This typology is used to add a second level of structure to Type I.

b = bilateral intergovernmental organization
c = conference series
d = dissolved, dormant
e = commercial enterprise
f = foundation, fund
g = intergovernmental
j = research institute
n = has become national
p = proposed body
s = information suspect
v = individual membership only
x = no recent information received
y = international organization membership