What are the Mossos d'Esquadra for hosts?
The Mossos d'Esquadra are Catalonia's own police force, and they run their own system for registering guests in tourist accommodations in Catalonia. If you own a holiday rental here, you may have to report bookings to both the state SES and the autonomous Mossos register.
The Mossos d'Esquadra are the police force of the Generalitat de Catalunya: same job as the National Police or Guardia Civil, but only in Catalonia. In tourism matters they run a guest register that already existed before the state-level SES, based on the Llei 13/2002 de turisme de Catalunya and developed by Decret 75/2020.
In 2021 the central government launched SES.Hospedajes (RD 933/2021). That opened a debate: do you report to Mossos, to SES, or to both? The practical answer the sector is applying is comply with both while the competence conflict remains unresolved, because the Catalan rules have not been repealed and Generalitat inspections still fine hosts who skip the regional register.
What you must report and to whom is set by Catalan law — not by the state Royal Decree. If you want to put SES and Mossos fields side by side, always check the current text of the relevant annex, because the two administrations have updated their forms independently of each other.
Fines in Catalonia are set by Llei 13/2002 de turisme (Title VI), with three levels: lleus (minor), greus (serious) and molt greus (very serious). The exact amounts are updated by the Generalitat from time to time — verify the current figures in the consolidated text on the Portal Jurídic de la Generalitat before assuming a range.
Why it matters
If you own a holiday home in Catalonia and you only comply with the state SES, the Mossos can fine you separately for skipping their register — two administrations, two independent sanctions. And note: registering a guest (Mossos) is not the same as holding the Catalan tourist licence (the famous HUT number). They are parallel obligations and you need both.