The first detailed statistical study of the Spanish Inquisition was the brainchild of Gustav Henningsen. Together with Jaime Contreras he registered 40.000 trials from the case summaries known as relaciones de causas, and supplemented these with data from Jean-Pierre Dedieu to publish a statistic of 44.000 trials. The resulting physical card index file had a basic statistical purpose, in accordance with the Inquisitorial historiography and the limited technical resources of that time. It was case-typological, and every trial record was therefore reduced to date (or year), court, main offence and sentence class. Most notably, defendants’ names and gender were excluded.

The EMID is the initiative of Gunnar W. Knutsen who started registering trial data from the Spanish Inquisition in a database in 1997. Using the index cards provided by Gustav Henningsen as a starting point he expanded the registration to a wider range of data and added more information from dispersed sources.

In 2011 this was supplemented by data from Jean-Pierre Dedieu’s registration of trials from Toledo, and the information was migrated to a new database structure originally designed by Dedieu.

In 2013 Mauricio Drelichman became involved in the work, and the decision was made to replace all the data registered by Henningsen and Contreras by registering everything from the start again from the original sources; so as to include names and details on proceedings, in accordance with newer historiographical guidelines. By so doing, the EMID shifted the emphasis of the database from statistical purposes to a documentary tool which made possible a far broader range of analysis

Since 2013 data on tens of thousands of trials has been registered by researchers and research assistants working in the AHN. At the hight of activity five people were working full time in the archive. The work is still in progress in this and other archives.

In 2015 data on more than 31.000 trials in the Portuguese Inquisition was added from the records of the Portuguese National Archives. Cleaning and coding of this data is ongoing.

After registration the registered trials are checked for errors, and duplicates are coded so that the various sources point to a single registered instance of a trial. Complicities, multiple trials, and family relationships between defendants are also registered. This is time consuming work that will have to be completed before the publication of EMID.