The objective of the U20 is to bring urban issues to the forefront of the G20 agenda. The U20 is both a unique platform and a call to action for ambitious, local government leaders to step up and send a joint message from U20 Cities for global climate action and sustainable development to national leaders, among others. Commitments and messages from the U20 are shared with the G20 Presidency and heads of states.

The U20 was developed in 2017 at the One Planet Summit in Paris under the leadership of the Mayor of Buenos Aires, Horacio Rodríguez Larreta, and the Mayor of Paris, Anne Hidalgo. This is a dedicated engagement group for city leaders to jointly engage national leaders and heads of state at the G20. The first U20 Summit was hosted by Buenos Aires in 2018 followed by Tokyo in 2019. Riyadh presides over the third U20 Summit where it aims to raise the ambition of participating cities and to accelerate action for sustainable urban development.

As of 2019, the U20 unites a globally leading group of 27 participating cities. Together, the U20 cities have a population of over 230 million, larger than the fifth most populous country in the world. They are responsible for over 8% of the global GDP and collectively constitute the world's third-largest economy.

Each U20 city represents a major economic or political powerhouse in a G20 country. The U20 Mayors Summit in Riyadh will leverage the combined power of the participating cities to a lasting impact on sustainable urban development.