What is retroactivity?
Retroactivity is the effectiveness of a standard at a time prior to its publication. That is, that a new regulatory provision affects past situations or events before it existed.
Retroactivity can have positive or negative consequences for the subjects affected by the norm, depending on whether it benefits or harms them.
For example, if a law reduces the penalty for a crime, and it is applied retroactively to those convicted of that crime before it came into force, favorable retroactivity occurs. But if a law increases the penalty for a crime, and it is applied retroactively to those convicted of that crime before it came into force, unfavorable retroactivity occurs.
The general rule in Spanish legislation is the non-retroactivity of regulations, unless otherwise provided. That is, the rules only apply to events after their entry into force, and do not affect the rights acquired under the previous rule.