Although its scope is determined by the constitution of each country, criminal law is generally based on the principle of legality. It is therefore common ground that an offence can be regarded as such only if the law expressly so provides. Thus, the principle of legality prevents a person from being arbitrarily accused and convicted of a crime. Legality, legal framework for the resolution of situations and disputes Starting from the general principle of legality, we find some variants and clarifications of this: The principle of legality already exists in the oldest societies, which began to write the laws that were previously maintained orally and that resulted from customs or traditions (customary rights). By putting the law in writing, it acquires a real entity, since its interpretation ceases to be arbitrary or fanciful and presupposes the submission of each individual to his existence. The laws of a society were created not only to resolve conflicts or disputes, but also for the purpose of organizing and ordering daily life in countless aspects, which can range from commercial and civil life to religious, family or individual life. Legality as a value is a set of beliefs, values, norms, and actions that encourage people to believe in the rule of law and reject injustice. Legality as a value allows us to appreciate the respect and interests of the legal system on the part of individuals and those who apply the law. In its original approach, the public administration could not act arbitrarily according to the principle of legality, but by implementing the content of the law. This was due to a strict interpretation of the principle of separation of powers, which had its origins in the French Revolution. Legality is a condition that refers to a situation that falls within the postulates of the law. In general, the term applies to situations where there is a clear circumstance that is free from objection in this regard.

When something is legal, it is supposed to correspond to the rights granted by a particular jurisdiction. However, that circumstance does not preclude the existence of various restrictions on existing rights, the exceeding of which could constitute a circumstance of illegality. In all cases, the scope and limits of each warranty are defined by law. Within the framework of the principle of legality, it acts in conjunction with the principle of the general interest, according to which the private interest must give way to the public or social interest, and with the principle of the separation of powers, according to which the public authority is divided into bodies with specific and limited functions for each of them. It should be noted that men and women living in a society where the culture of legality is practiced have committed themselves to developing the following actions: It is known as the principle of legality for the precedence of the law over any activity or function of public authority. This means that everything that emanates from the state must be regulated by law and never by the will of the individual. The principle of legality is to guarantee and protect legal certainty. Although it is used throughout the legal system, it is gaining importance in the criminal, administrative and tax fields. In most countries, criminal law is based on the principle of legality. This means that a crime is listed only as long as the law expressly provides for it. In some cases, the legality of a particular circumstance may be doubtful, as there is a legal or grey vacuum in this regard, making the existence of a situation of anomaly or transgression legally questionable. In fact, laws tend to be general and therefore cannot cover all the cases that may arise, it is the case law that fills these gaps; However, the case can sometimes be new and must require a prior analysis of the clarification.

In general, this implies that all public authorities and citizens are subject to the law and can only do what is or is not prohibited by law. The principle of legality is linked to other general principles of law. If a particular behavior does not fall within a parameter that the law establishes as illegal, the truth is that this behavior is considered legal, even if the act in question is morally questionable. Lawfulness in this sense is justified by the fact that a particular activity must be legally recognized as negative before such conduct occurs. Similarly, there must be due process that establishes that a particular situation has been developed in a way that contradicts what has been determined from a legal point of view. After all, it is impossible to apply laws retroactively, that is, to blame a person for doing a particular act before passing a law condemning such an act. In the case of Spain, the principle of legality is set out in the provisional title of the 1978 Constitution. Thus, Article 9.3 on the principles of the legal order of the person in question is set out in Article 9.3. In particular, it is specified that, like these others, it is fully guaranteed: the principle of legality or primacy of the law is a fundamental principle according to which any exercise of public authority must be carried out in accordance with the law in force and not according to the will of the people.

If a state adheres to this principle, then the actions of its power are subject to the constitution and the current state or rule of law. Legality and legitimacy are 2 of the major concepts of political theory.