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Ratification is a principal's approval of an act of its agent where the agent lacked authority to legally bind the principal. The term applies to private contract law, international treaties, and constitutionals in federations such as the United States and Canada.
Private law 
In contract law, the need for ratification can arise in two ways: where the agent attempts to bind the principal despite lacking the authority to do so, and where the principal authorizes the agent to make an agreement, but reserves the right to approve it. An example of the first situation is where an employee not normally responsible for procuring supplies contracts to do so on the employer's behalf. The employer's choice on discovering the contract is to ratify it or to repudiate it.
The other situation is common in trade union collective bargaining agreements. The Union authorizes one or more people to negotiate and sign an agreement with management. A collective bargaining agreement can not become legally binding until the union members ratify the agreement. If they do not approve it, the agreement is of no effect, and negotiations resume.
Ratification of an international treaty 
The ratification of international treaties is accomplished by filing instruments of ratification as provided for in the treaty. In most democracies, the legislature authorizes the government to ratify treaties through standard legislative procedures (i.e., passing a bill).
United Kingdom 
In the UK, treaty ratification was a Royal Prerogative, exercised by Her Majesty on the advice of her Government. But, by a convention called the Ponsonby Rule, treaties were usually placed before parliament for 21 days before ratification. This was put onto a statutory footing by the Constitutional Reform and Governance Act 2010.
United States 
In the US, the treaty power is a coordinated effort between the Executive branch and the Senate. The President may form and negotiate, but the treaty must be advised and consented to by a two-thirds vote in the Senate. Only after the Senate approves the treaty can the President ratify it. Once a treaty is ratified, it becomes binding on all the states under the Supremacy Clause. While the United States House of Representatives does not vote on it at all, the requirement for Senate advice and consent to ratification makes it considerably more difficult in the US than in other democratic republics to rally enough political support for international treaties. Also, if implementation of the treaty requires the expenditure of funds, the House of Representatives may be able to block, or at least impede, such implementation by refusing to vote for the appropriation of the necessary funds.
In the US, the President usually submits a treaty to the Senate Foreign Relations Committee (SFRC) along with an accompanying resolution of ratification or accession. If the treaty and resolution receive favorable committee consideration (a committee vote in favor of ratification or accession) the treaty is then forwarded to the floor of the full U.S. Senate for such a vote. The treaty or legislation does not apply until it has been ratified. A multilateral agreement may provide that it will take effect upon its ratification by less than all of the signatories. Even though such a treaty takes effect, it does not apply to signatories that have not ratified it. Accession has the same legal effect as ratification. Accession is a synonym for ratification for treaties already negotiated and signed by other states. An example of a treaty to which the U.S. Senate did not advise and consent to ratification is the Treaty of Versailles, which was part of the resolution of the First World War.
In Australia, power to enter into treaties is an executive power within Section 61 of the Australian Constitution. Thus the Australian Federal Government may enter into a binding treaty without seeking parliamentary approval. However, implementation of treaties does require legislation by Federal parliament, following Section 51(xxix) of the Australian Constitution and signed by the Governor-General of Australia.
In Japan, in principle both houses of the parliament (the National Diet) must approve the treaty for ratification. In the event the Upper House (House of Councilors) rejects a treaty approved by the Lower House (House of Representatives) and a joint committee of both houses cannot come to agreement on amendments to the original text of the treaty, or the Upper House fails to decide on a treaty for more than thirty (30) days, by the Constitutional supremacy of the House of Representatives the decision by the Upper House will be regarded as the vote of the National Diet approving the ratification. The approved treaty will then be promulgated into law by the Constitutional act of the Emperor.
Ratification of a constitution 
Federations usually require the support of both the federal government and some given percentage of the constituent governments for amendments to the federal constitution to take effect.
Ratification of the United States Constitution 
Article Seven of the constitution of the United States describes the process by which the entire document was to become effective. It required that conventions of nine of the thirteen original States ratify the constitution. Once word was received that the ninth state had ratified the constitution—New Hampshire, June 21, 1788—a timetable was set for the start of operations under the Constitution, and on March 4, 1789, the government under the Constitution began operations.
- An example for such a treaty can be seen in the Convention on Cluster Munition. It will enter into force as soon as it has ben ratified by at least 30 states. See Article 17 of the Convention on Cluster Munitions.
- United Nations Treaty Collection, Treaty Reference Guide(1999)