This report describes the rules that were established in the creation of the EuroFIR Thesauri, which is a set of standard vocabularies recommended for data exchange and management. Each thesaurus is made up of descriptors and, generally, further elaborated with additional information. The different thesauri that contribute to the EuroFIR Thesauri are listed and each thesaurus is composed of a list of word and their meanings in this context according to 'similarity of meaning' so it can be determined which criteria were used to build them. These include: Acquisition thesaurus: categories for the origin of values Reference thesaurus: details of bibliographical references of data sources Component thesaurus: descriptors used to identify the physic-chemical property of data Unit thesaurus: information about the measure used for properties Matrix unit thesaurus: terms for the amount of matrix material, usually expressed preposition per Value thesaurus: further describe data value or give a quality description of the value when no value can be given Method thesaurus: general indication of the type of method used Key words Code: unique and short alphanumeric code identifying each concept Descriptor: text describing the concept Scope Note: note attached to a descriptor to indicate its meaning Additional Information: note attached to a descriptor to provide definitions and links to authoritative sources