CO 2 -Responsive polymer materials have received enormous attention in recent years, since CO 2 as a new trigger has many advantages such as abundant availability, low cost, energy-saving, environment-friendly, non-toxic, good reversibility as well as great biocompatibility. In this review, we first discuss the virtues of CO 2 -responsiveness by comparing with traditional stimuli-sensitive materials that respond to pH, light, or redox stimuli. Then, the chemical fundamentals of CO 2 -responsive polymer materials are revealed including recently discovered "unexpected" CO 2 -sensitive features. Recent progress of CO 2 -responsive polymer materials is highlighted followed by various CO 2 -responsive "smart" polymer systems. Finally, challenges and outlooks in this area are discussed. This paper reviews the chemical fundamentals of CO 2 -responsive polymers as well as the latest reported "smart" material systems switched by CO 2 .