In the U.S., a notary provides legal verification of an individual's signature in business and legal transactions. In foreign countries, a notary does the same, but often has broader powers. Many countries require notaries to be trained in law, some require notaries to be lawyers also, and some have different types of notaries whose authority to certify certain documents depends on their training. For example, a foreign notary might prepare legal documents, do a title search, certify title, translate documents, certify translations, and file and register documents with government authorities. Foreign notarial fees are commonly higher than those in the U.S. because of the extended services provided.

A  notary is a public officer constituted by law to serve the public in non-contentious matters usually concerned with wills, estates, deeds, powers-of-attorney, and foreign and international business. A notary's main functions are to administer oaths and affirmations, take affidavits and statutory declarations, witness and authenticate the execution of certain classes of documents, take acknowledgements of deeds and other conveyances, protest notes and bills of exchange, provide notice of foreign drafts, prepare marine protests in cases of damage, provide exemplifications and notarial copies, and perform certain other official acts depending on the jurisdiction. Any such act is known as a notarization.

With the exceptions of Louisiana, Puerto Rico, and Quebec, whose private law is based on civil law, a notary public in the rest of the United States and most of Canada has powers that are far more limited than those of civil-law or other common-law notaries, both of whom are qualified lawyers admitted to the bar: such notaries may be referred to as notaries-at-law or notary lawyers. Therefore, at common law, notarial service is distinct from the practice of law, and giving legal advice and preparing legal instruments is forbidden to lay notaries.

Notaries are appointed by a government authority, such as a court or lieutenant governor, or by a regulating body often known as a Society or Faculty of Notaries Public. For a notary-at-law, an appointment is usually for life, but lay notaries are commissioned for a briefer term with the possibility of renewal. Appointments and their number for a given notarial district are highly regulated. Since the majority of American notaries are lay persons, however, commissions are not regulated, which is why there are far more notaries in the United States than in other countries.

For the purposes of authentication, most countries require commercial or personal documents which originate from or are signed in another country to be notarized before they can be used or officially recorded or before they can have any legal effect. To these documents a notary affixes a notarial certificate which attests to the execution of the document, usually by the person who appears before the notary, known as an appearer or constituent. In places where notaries-at-law are the norm, a notary may also draft legal instruments known as notarial acts which have probative value and executory force as would any lawyer's writing. Originals or duplicate originals are then filed and stored in the notary's archives, or protocol.

Notaries in some countries and states are required to undergo special training in the performance of their duties. Many must also first serve as an apprentice before being commissioned or licensed to practice their profession. In many countries, even licensed lawyers, e.g., barristers or solicitors, must follow a prescribed specialized course of study and be mentored for two years before being allowed to practice as a notary. Notaries public in the United States, of which the vast majority are lay people, may not engage in any activities that could be construed as the practice of law unless they are also a qualified attorney.

In civil or bi-juridical jurisdictions, such as South Africa, the Office of notary public is a legal profession with educational requirements similar to those for lawyers. Many even have institutes of higher learning who offer degrees in notarial law.