Adverse possession is a legal concept that converts continuous and qualified possession of an asset into ownership. It is a fundamental concept in Catalan civil law that recognises a fact: anyone who has possessed an asset for many years, publicly, peacefully and as the owner, may end up acquiring legal ownership, even if they did not initially have formal title.

The essential requirements for consolidating ownership through adverse possession are:

• Possession as owner (not as tenant, depositary or in any other capacity).

• Public possession (not hidden).

• Peaceful possession (without opposition).

• Uninterrupted possession during the legal period.

In Catalonia, the general period is 20 years for ordinary adverse possession. Under state law, it is 30 years for extraordinary adverse possession.

It can occur in many cases. Fields and farms that are passed down from parents to children ‘de facto’, without a written title, but which have been cultivated and maintained for generations. Old developments where parking spaces were sold in undivided shares without a deed for each space. Property with lost or non-existent titles. The owners and then their heirs have used, exploited and rented them for decades.

Adverse possession is not automatically registered in the Land Registry: a formal title is required to do so. There are three main ways:

Notarial certificate of notoriety, when there is sufficient evidence and no one objects. However, there are many exceptions; it depends on the registrar's discretion (who may require additional documentation or deem the file incomplete). It is suspended if any interested party objects, it is not valid for recent transfers without a deed, and it is necessary to specify when and how the property was acquired with clear evidence.

Notarial title deed, regulated mainly by Article 203 LH for the registration of properties and by Article 208 LH for the resumption of interrupted succession. This procedure is more formal and offers greater guarantees, but it is also more complex and requires strict compliance with the established procedural requirements.

Legal claim for declaration of ownership, when there is opposition or a lack of clear documentary evidence.

 In conclusion, adverse possession is a tool that allows many old situations to be put in order and provides legal certainty: what has been owned and used as one's own for decades ends up being recognised as such by a title deed and can therefore be registered in the Land Registry.