According to the ISO 5963 (1985) standard, indexing is the process of describing or representing the thematic content of an information resource.

This process results in an index of indexing terms that will be used as a search and access tool to the content of resources in information retrieval systems.

Indexing is a technical-intellectual activity made up of procedures aimed at breaking down, deciphering, analyzing and summarizing the content of documents, all with the aim of making possible the storage, recovery, access and dissemination of information, facilitating its recovery, either directly by users or through indexes, catalogues, databases, etc., and is carried out in a controlled and standardized manner through a process made up of four stages:

This conception of indexing, whose central elements are the human determination of the topic and the assignment of terms from a controlled vocabulary, distinguishes it from automatic indexing and free indexing.

Automatic indexing is pull indexing.

Keywords are extracted from the title, summary or full text of a resource, and used to represent its content, without being subjected to any type of terminological control.

The articles "Article (grammar)"), conjunctions "Conjunction (grammar)"), pronouns, prepositions, interjections, numerals "Numeral (linguistics)") and some verbs and adverbs are stop words. Nouns, adjectives and some verbs and adverbs are non-empty words.

Free indexing is one that does not use, in the representation of topics, terms from a controlled vocabulary but rather uses terms extracted from the resource itself or from the mind of the indexer.

By indexing policy we understand both the way of indexing a given institution and the effort to specify, systematize and capture in guides or manuals the processes followed in indexing.

Example of a general indexing policy for a library:.