MIAR is a matrix of data from more than 100 international indexing and abstracting databases (citation, multidisciplinary or specialised databases) and journal repertoires, which is developed with the purpose of providing useful information for the identification of scientific journals and the analysis of their diffusion. The system works through the elaboration of a correspondence matrix between the journals, identified by their ISSN, and the databases and directories that index or include them.

MIAR has more than 48,000 journal records, but a search in MIAR using a valid ISSN number will return information on the diffusion of any journal in the world at the sources analysed by MIAR, whether or not it has its own record in MIAR.

If a journal passes the MIAR inclusion threshold (which consists of the journal being present in at least one of the sources analysed), the record for that journal with which it will be registered will contain a series of descriptive data on the publication as well as the link to the websites of the sources in which it is found to be present. Journals are grouped into broad scientific fields, further subdivided into more specific academic fields.

For the journals included in MIAR, each and every one of the sources in which their presence is traced is reported in detail, indicating the date of verification. As a summary of the journal's diffusion, the expression cN+mN+eN+xN describes the N occurrences observed in the four categories of sources analysed: citation databases (c), multidisciplinary (m), specialised (e) and evaluation resources (x).

The expression cN+mN+eN+xN replaces the ICDS^* indicator used by MIAR until 2021. The new way of presenting diffusion through this expression is clearer and more descriptive, although it is generated from the same information that fed the ICDS, as it reports the number and type of sources where a journal is present. This change responds to the desire to make MIAR an aggregator of information from different sources, with the aim of supporting authors, publishers and other agents who need to identify, characterise and analyse journals, but without calculating any bibliometric indicator from the information collected.

MIAR welcomes contributions from editors, authors and readers, who may suggest new journals, or make contact to report errors, ask questions or give feedback.

The MIAR Live version is updated semesterly (end of June and end of December) based on the data available for each information source. A closing edition is also provided for every year since 2008.

* Note on the ICDS: The ICDS (Composite Index of Secondary Diffusion) is offered for each journal in case of the closed annual editions of MIAR for the years 2008 to 2021. It was an indicator designed as a synthetic way of showing the diffusion of a journal in different scientific databases of international scope, or otherwise in repertories of evaluation of periodicals. A high ICDS meant that the journal was present in different sources of information of international relevance. The following criteria were used to calculate the ICDS:

• If the journal appeared in the citation indexes of the Web of Science Core Collections (AHCI, SCIE, SSCI or ESCI) or in Scopus, a score of 3.5 was assigned.
• If the journal appeared in the Web of Science flagship citation indexes (AHCI, SCIE or SSCI) and simultaneously in Scopus, a score of +1 was assigned. 
• If the journal appeared in a single indexing and abstracting database (specialised or multidisciplinary), or in DOAJ, a score of +3 was assigned. However, if the journal was included in two or more specialised or multidisciplinary databases, a total of 5 points (3+2) was assigned.
• If it did not appear in any indexing database but in the Latindex catalogue (not to be confused with the Latindex directory) or in an evaluation directory (CARHUS Plus, ERIHPlus, REDIB or FECYT quality seal), a score of 2.5 was assigned.
• If it appeared only in DIALNET, 0.4 points were assigned. 
• Finally, the calculation was completed with the journal's survival index, calculated as the logarithm of the total number of years of life of the title since the beginning of its publication, considering a maximum of 30 years in the calculation.