“Criminal law is not only an art—the least known, undoubtedly the most tragic—but also the most contemporary of all arts.”
— Jacques VERGES

Criminal law is the body of rules that defines human behaviors considered as crimes and the corresponding sanctions applicable to them. The purpose and function of criminal law is set out in Article 1 of the Turkish Penal Code No. 5237:

"The purpose of the penal code is to protect individual rights and freedoms, public order and safety, the rule of law, public health and the environment, and social peace, as well as to prevent the commission of crimes. The Code regulates, for this purpose, the fundamental principles of criminal liability, offenses, types of punishments and security measures."

Criminal law is divided into three main branches: substantive criminal law, criminal procedural law, and criminal enforcement law.

Substantive criminal law examines which acts constitute crimes, the elements of offenses, conditions for punishment, types of penalties, and the basic principles governing them. The primary legislation in this field is the Turkish Penal Code No. 5237. Substantive criminal law is further divided into general provisions and specific provisions. Accordingly, the Code contains a "General Provisions" section (Articles 1–75) covering principles of criminal law, the scope of its application, international criminal law principles, theory of crime (including elements of offenses, conditions for punishment, attempt, participation, and accumulation rules), and sanctions (including penalties and security measures), as well as rules for determining and individualizing penalties, case dismissal, and complaint or prepayment procedures. The "Specific Provisions" section (Articles 76–343) deals with defined criminal offenses and associated sanctions, such as intentional homicide, assault, and sexual offenses.

Criminal procedural law governs the investigation and prosecution process following suspicion of a crime, determining whether a punishable act has actually occurred, by whom, and in what manner. It also regulates the procedural application of penalties and security measures to the specific case. Criminal procedure consists of investigation and prosecution stages. The parties involved are the prosecution (public prosecutor), the defense (suspect/accused and counsel), and the judicial authority. Victims or injured parties participate in the proceedings as complainants, while the prosecution is primarily a public action. Measures such as detention, arrest, search and seizure, and wiretapping are procedural instruments. The main legislation is the Turkish Criminal Procedure Code No. 5271, effective since 2005.

Criminal enforcement law regulates the execution of sanctions imposed following a criminal conviction. It covers the type of penal institution where imprisonment is served, the commencement and completion of sentences, and provisions for conditional release. The fundamental legislation is the Law on the Execution of Sentences and Security Measures No. 5275, effective from December 13, 2004.