Article 50 of the Treaty on European Union (TEU) is a provision that outlines the process by which a member state can voluntarily withdraw from the European Union. It was introduced by the Treaty of Lisbon, which came into force on December 1, 2009. Article 50 has gained significant attention and importance in the context of the United Kingdom’s decision to leave the European Union, commonly known as Brexit.

Here is the text of Article 50:

> “1. Any Member State may decide to withdraw from the Union in accordance with its own constitutional requirements.
> 2. A Member State which decides to withdraw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218(3) of the Treaty on the Functioning of the European Union. It shall be concluded on behalf of the Union by the Council, acting by a qualified majority, after obtaining the consent of the European Parliament.
> 3. The Treaties shall cease to apply to the State in question from the date of entry into force of the withdrawal agreement or, failing that, two years after the notification referred to in paragraph 2, unless the European Council, in agreement with the Member State concerned, unanimously decides to extend this period.
> 4. For the purposes of paragraphs 2 and 3, the member of the European Council or of the Council representing the withdrawing Member State shall not participate in the discussions of the European Council or Council or in decisions concerning it.
> A qualified majority shall be defined in accordance with Article 238(3)(b) of the Treaty on the Functioning of the European Union.
> 5. If a State which has withdrawn from the Union asks to rejoin, its request shall be subject to the procedure referred to in Article 49.”

Key points regarding Article 50 include:

1. **Voluntary Withdrawal:** The decision to withdraw from the EU is entirely voluntary and can be made by any member state in accordance with its own constitutional processes.

2. **Notification:** Once a member state decides to withdraw, it must formally notify the European Council of its intention.

3. **Negotiation:** The EU then engages in negotiations with the withdrawing member state to establish the terms of its withdrawal, including arrangements for the future relationship between the withdrawing state and the EU.

4. **Two-Year Timeframe:** Unless an extension is agreed upon unanimously by the European Council and the withdrawing state, the Treaties cease to apply to the withdrawing state two years after the notification is made. This timeframe can be extended if both parties agree.

5. **Exclusion from Decision-Making:** During the negotiation period, the withdrawing state’s representative is excluded from discussions and decisions directly affecting the state.

6. **Rejoining Procedure:** If a state that has withdrawn wishes to rejoin the EU, it must go through the accession process outlined in Article 49 of the Treaty on European Union.

Article 50 was invoked by the United Kingdom in March 2017, triggering the Brexit process. The UK officially left the EU on January 31, 2020, and the transition period ended on December 31, 2020. The provisions of Article 50 played a crucial role in shaping the negotiations and the eventual withdrawal agreement between the UK and the EU.