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Penitentiary law: what it regulates and why it is not the same as criminal law

Penitentiary law: what it regulates and why it is not the same as criminal law

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Written by Pardo Geijo Abogados

Published: June 10, 2026

Penitentiary law: what it regulates and why it is not the same as criminal law

When a person is sentenced to prison and enters the penitentiary system, the law does not disappear: it changes protagonist. Criminal law, which governed the process from the investigation to the judgment, takes a back seat, and another, less well-known but decisive, branch of law enters the scene for the convicted person's life from that moment on: penitentiary law.

Penitentiary law is the discipline that regulates the enforcement of custodial sentences, the functioning of penitentiaries, the rights and duties of inmates and the treatment system oriented towards reintegration. It comprises three dimensions: the institutional, concerning the organisation of the penitentiary system; that of the inmate's rights and duties; and that of treatment, which covers classification into grades, the individualised plan, leaves and parole. Its axis is Article 25.2 of the Constitution, which directs custodial sentences towards re-education and social reintegration.

Its normative sources form a hierarchical system: the Constitution, with its Articles 15 and 25.2; the General Penitentiary Organic Law of 1979, the central rule; the Penitentiary Regulations of 1996, which develop the practical aspects; and European regulations, such as the European Prison Rules and the case law of the European Court of Human Rights.

Although penitentiary law arises from criminal law, they are distinct disciplines. Criminal law regulates offences and penalties: its focus is on the past and on the determination of responsibility. Penitentiary law regulates the enforcement of the sentence: its focus is on the present and the future, on treatment and reintegration. Criminal law operates during the investigation, prosecution and conviction, before the criminal courts; penitentiary law operates during enforcement, before the penitentiary administration and the prison supervision judge. Each is governed by its own principles: penitentiary law adds the individualisation of treatment, progressiveness and humanity.

An essential aspect of penitentiary law is that the deprivation of liberty does not amount to the loss of all rights. The inmate retains their fundamental rights, except those incompatible with the deprivation of liberty: they keep the right to physical and moral integrity, to privacy compatible with the regime, to confidential communication with their lawyer, to healthcare, to education, to communicate with relatives, to practise their religion and to appeal the administration's decisions. What is essentially suspended is freedom of movement, the proper content of the penalty.

The central figure of penitentiary law is the prison supervision judge, created by the General Penitentiary Organic Law to oversee the lawfulness of the service of sentences and to protect inmates. They resolve inmates' complaints and appeals, approve or refuse leaves, decide on classification and grade progression, control disciplinary sanctions and rule on parole. They are the arbiter who balances the authority of the penitentiary administration with the inmate's rights.

Owing to its technical complexity, penitentiary law is a specialisation within the criminal field in which the lawyer's experience makes a significant difference. In matters such as the accumulation of sentences, the review of the sentence calculation or appeals before the supervision judge, having a lawyer who masters the subject can have a very concrete impact on the effective duration of the deprivation of liberty.

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