Public law (lat. iuspublicum) is that part of law which governs relationships between individuals and the government, and those relationships between individuals which are of direct concern to the society. Public law comprises constitutional law,administrative law, tax law and criminal law, as well as all procedural law. In public law, mandatory rules (not optional) prevail. Laws concerning relationships between individuals belong to private law.

The relationships public law governs are asymmetric and unequal – government bodies (central or local) can make decisions about the rights of individuals. However, as a consequence of the rule of law doctrine, authorities may only act within the law (secundumet intra legem). The government must obey the law. For example, a citizen unhappy with a decision of an administrative authority can ask a court for judicial review.

Rights, too, can be divided into private rights and public rights. A paragon of a public right is the right to welfare benefits – only a natural person can claim such payments, and they are awarded through an administrative decision out of the government budget.

The distinction between public law and private law dates back to Roman law. It has been picked up in the countries of civil law tradition at the beginning of the 19th century, but since then spread to common law countries, too.

The borderline between public law and private law is not always clear in particular cases.