Law is a system of rules created and enforced through social or governmental institutions to regulate behavior. Its principal purposes are establishing standards, maintaining order, resolving disputes and protecting liberty and rights. It shapes politics, economics, history and society in many ways. Law can be made by a collective legislature, resulting in statutes; by the executive, in decrees and regulations; or through precedent established by judges in common law jurisdictions.

In addition to criminal laws, the law also covers such matters as contracts, property and taxes. Some areas of law are very complex. For example, tax law involves rules governing the amount of value added and corporate taxes; banking law includes rules about capitalization and liabilities; and space law addresses issues related to human activity in Earth orbit and outer space.

A judge may decide a case without a jury or by hearing from witnesses and receiving written evidence. An indictment is the formal charge from a grand jury that there is sufficient evidence to convict the defendant of a crime. A court can hear a case in federal court only if it has subject matter jurisdiction over the issue. A lawyer may present exculpatory or inculpatory evidence to support the case for his client.

The rule of law requires government to adhere to international human rights and other standards. It also requires adherence to principles of supremacy of law, equality before the law, accountability to the law, participation in law-making and legal certainty.