From the construction times (1993) to the creation of the company, THEMIS has been a joint operation between Spain, Italy, and France, ruled by several agreements at international level, mostly:

• An international treaty about “Astrophysics in the Canary Islands” linking France and Spain. This treaty is threefold, from level 1 (member states) to level 3 (institutes, in this case the Instituto de Astrofisica de Canarias (IAC) and the “Centre National de la Recherche Scientifique” (CNRS), and has different lifetimes depending on the level of the agreement
• A convention regulating the use and exploitation of the installation between the Italian Consiglio Nazionale delle Ricerche (CNR) and the French CNRS, and valid until 2009.

THEMIS has been treated by the CNRS as a “Très Grand Equipement” (TGE facility) until 2008. Since this moment it has been managed and financed by the Institut National des sciences de l'Univers (INSU), an institute of the CNRS.

The private company THEMIS, S.L. is owned and has been operated jointly by France and the Italy public research entities to allow for a rational and moneywise exploitation and maintenance of the telescope, located withing the Teide Observatory of the Instituto de Astrofisica de Canarias in the Canary Islands.

The THEMIS Limited Company (THEMIS S.L.) has been created on March 2000, 23rd as a Spanish rights company, and is registered at the Tenerife Trade Register Board with CIF B-38583886. Although it has regular commercial statutes, it actually acts as a non-profit organization, having a capital of 3016 euros. The shareholders (owners of the company) are the French “Centre National de la Recherche Scientifique” (CNRS) for 80%, and the Italian “Consiglio Nazionale delle Ricerche” (CNR) for 20%.

Since July 2018, THEMIS S.L.U , a uni-personal limited society registered at the Tenerife Trade Register Board with CIF B-38583886 is the successor of the former company. This new structure is 100% owned and subsidized by the CNRS/ INSU.

Since 1998, the CNRS has been maintaining an administrative unit located in La Laguna to make possible the continuous presence of french public employees (engineers and scientists) on the THEMIS telescope site. This unit was initially created as a “Unité Propre de Service” (service unit) UPS853. This unit was later converted in UPS3718 without big changes. Since 2020, a much more significant structure has been created as a joint initiative between the Instituto de Astrofisica de Canarias (IAC) and the CNRS. This new structure is an international research laboratory (IRL) named after “French-Spanish Laboratory for Astrophysics in the Canarias” FSLAC , or IRL2009. FSLAC has wider scientific objectives than the former service-only structures, and can potentially host more personal.