The Chinese Academy of Sciences (CAS) is the national academy for the natural sciences of the People's Republic of China. It has historical origins in the Academia Sinica during the Republican era and was formerly also known by that name.

Collectively known as the "Two Academies" along with the Chinese Academy of Engineering, it functions as the national scientific think tank and academic governing body, providing advisory and appraisal services on issues stemming from the national economy, social development, and science and technology progress. It is headquartered in Xicheng District, Beijing, with branch institutes all over mainland China. It has also created hundreds of commercial enterprises, Lenovo being one of the most famous.

It is the world's largest research organization, comprising around 60,000 researchers working in 114 institutes, and has been consistently ranked among the top research organizations around the world.

The Chinese Academy of Sciences has been consistently ranked the No. 1 research institute in the world by Nature Index since the list's inception in 2016 by Nature Research. It is the most productive institution publishing articles of sustainable development indexed in Web of Science from 1981 to 2018 among all universities and research institutions in the World.

The Chinese Academy of Sciences (CAS) in Beijing has topped the Nature Index 2020 Annual Tables list as the most prolific producer of research published in the 82 selected journals tracked by the Index.