Legal systems elaborate rights and responsibilities in a variety of ways. A general distinction can be made between civil law jurisdictions, which codify their laws, and common law systems, where judge made law is not consolidated. In some countries, religion still informs the law. In a typical democracy, the central institutions for interpreting and creating law are the three main branches of government, namely an impartial judiciary, a democratic legislature, and an accountable executive. To implement and enforce the law and provide services to the public, a government's bureaucracy, the military and police are vital.

International law can refer to three things: public international law, private international law or conflict of laws and the law of supranational organizations. Public international law concerns relationships between sovereign nations. The sources for public international law development are custom, practice and treaties between sovereign nations, such as the Geneva Conventions. Public international law can be formed by international organizations, such as the United Nations, the International Labor Organization, the World Trade Organization, or the International Monetary Fund. Public international law has a special status as law because there is no international police force, and courts (e.g. the International Court of Justice as the primary UN judicial organ) lack the capacity to penalize disobedience. However, a few bodies, such as the WTO, have effective systems of binding arbitration and dispute resolution backed up by trade sanctions.

Constitutional and administrative laws govern the affairs of the state. Constitutional law concerns both the relationships between the executive, legislature and judiciary and the human rights or civil liberties of individuals against the state. Most jurisdictions, like the United States and France, have a single codified constitution, with a Bill of Rights. A few, like the United Kingdom, have no such document. A "constitution" is simply those laws which constitute the body politic, from statute, case law and convention.

The fundamental constitutional principle, inspired by John Locke, holds that the individual can do anything but that which is forbidden by law, and the state may do nothing but that which is authorized by law. Administrative law is the chief method for people to hold state bodies to account. People can apply for judicial review of actions or decisions by local councils, public services or government ministries, to ensure that they comply with the law.

Criminal law, also known as penal law, pertains to crimes and punishment. It thus regulates the definition of and penalties for offences found to have a sufficiently deleterious social impact but, in itself, makes no moral judgement on an offender nor imposes restrictions on society that physically prevents people from committing a crime in the first place. Investigating, apprehending, charging, and trying suspected offenders are regulated by the law of criminal procedure. The paradigm case of a crime lies in the proof, beyond reasonable doubt, that a person is guilty of two things. First, the accused must commit an act which is deemed by society to be criminal, or actus reus (guilty act). Second, the accused must have the requisite malicious intent to do a criminal act, or mens rea (guilty mind). However for so called "strict liability" crimes, an actus reus is enough. Criminal systems of the civil law tradition distinguish between intention in the broad sense (dolus directus and dolus eventualis), and negligence. Negligence does not carry criminal responsibility unless a particular crime provides for its punishment.