Classifications group and organize information meaningfully and systematically into a standard format that is useful for determining the similarity of ideas, events, objects or persons. It is made up of mutually exclusive and exhaustive categories, often presented as a hierarchy that is reflected by the numeric or alphabetical codes assigned to them. The categories "male" and "female" constitute a classification for the variable "sex", which can be observed for humans as well as for many other living organisms.

Classifications may be constructed to support the implementation of regulatory policies such as customs regulations or criminal legislation. They are also used to standardize concepts of public services such as job placement, education, welfare or public health and to describe social, economic or natural phenomena. When in general use these classifications are called standard classifications; and standard statistical classifications represent a subset used to organize and present statistics.

The ILO is custodian of two international classifications, which are part of the international family of economic and social classifications and for which it is responsible for their maintenance, updating and revision. These classifications are:

The ILO is also custodian of the:

These three classifications have been adopted by the International Conference of Labour Statisticians.

Other classifications of interest to labour statistics are: