Law is a system of rules, enforced through a set of institutions, used as an instrument to underpin civil obedience, politics, economics and society.

Law consists of a wide variety of separate disciplines. Contract law regulates binding agreements which may relate to everything from civil purchase to trading on derivatives markets.

Trust law applies to assets held for investment and financial security, while Tort law allows claims for compensation if an individual or their property is injured or harmed. If the harm is criminalised in penal code, criminal law offers means by which the state can prosecute the perpetrator.

Constitutional law provides a framework for the creation of law, the protection of human rights and the election of political representatives.

Legal systems elaborate rights and responsibilities in a variety of ways. A basic distinction is generally made between civil law jurisdictions and systems using common law. In some countries, religion informs the law. Scholars investigate the nature of law through many perspectives, including legal history and philosophy, or social sciences such as economics and sociology.

The study of law raises important and complex issues concerning equality, fairness, liberty and justice. "In its majestic equality", said the author Anatole France in 1894, "the law forbids rich and poor alike to sleep under bridges, beg in the streets and steal loaves of bread." 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.

While all these organs of the state are creatures created and bound by law, an independent legal profession and a vibrant civil society inform and support their progress.

All legal systems deal with similar issues and behaviors, but each country categorises and identifies its legal standards and principals in different ways.

A common distinction is that between "public law" (a term related closely to the state, and including constitutional, administrative and criminal law), and "private law" (which covers contract, tort and property). In civil law systems, contract and tort fall under a general law of obligations, while trusts law is dealt with under statutory regimes or international conventions.

International, constitutional and administrative law, criminal law, contract, tort, property law and trusts are regarded as the "traditional core subjects", although there are many further disciplines which may be of greater practical importance.

Prominent examples of legislatures are the Houses of Parliament in London, the Congress in Washington D.C., the Bundestag in Berlin, the Duma in Moscow, the Parlamento Italiano in Rome and the Assemblée nationale in Paris. By the principle of representative government people vote for politicians to carry out their wishes. Although countries like Israel, Greece, Sweden and China are unicameral, most countries are bicameral, meaning they have two separately appointed legislative houses.

In the 'lower house' politicians are elected to represent smaller constituencies. The 'upper house' is usually elected to represent states in a federal system (as in Australia or the United States) or different voting configuration in a unitary system (as in France).

In the UK the upper house is appointed by the government as a house of review. One criticism of bicameral systems with two elected chambers is that the upper and lower houses may simply mirror one another. The traditional justification of bicameralism is that an upper chamber acts as a house of review. This can minimise arbitrariness and injustice in governmental action.

To pass legislation, a majority of Members of Parliament must vote for a bill (proposed law) in each house. Normally there will be several readings and amendments proposed by the different political factions.

If a country has an entrenched constitution, a special majority for changes to the constitution will be required, making changes to the law more difficult. A government usually leads the process, which can be formed from Members of Parliament (e.g. the UK or Germany).

But in a presidential system, an executive appoints a cabinet to govern from his or her political allies whether or not they are elected (e.g. the United States or Brazil), and the legislature's role is reduced to either ratification or veto.