CO2-responsive materials undergo a change in chemical or physical properties in response to the introduction or removal of CO2. The use of CO2 as a stimulus is advantageous as it is abundant, benign, inexpensive, and it does not accumulate in a system. Many CO2-responsive materials have already been explored including polymers, latexes, surfactants, and catalysts. As a sub-set of CO2-responsive polymers, the study of CO2-responsive gels (insoluble, cross-linked polymers) is a unique discipline due to the unique set of changes in the gels brought about by CO2 such as swelling or a transformed morphology. In the past 15 years, CO2-responsive gels and self-assembled gels have been investigated for a variety of emerging potential applications, reported in 90 peer-reviewed publications. The two most widely exploited properties include the control of flow (fluids) via CO2-triggered aggregation and their capacity for reversible CO2 absorption-desorption, leading to applications in Enhanced Oil Recovery (EOR) and CO2 sequestration, respectively. In this paper, we review the preparation, properties, and applications of these CO2-responsive gels, broadly classified by particle size as nanogels, microgels, aerogels, and macrogels. We have included a section on CO2-induced self-assembled gels (including poly(ionic liquid) gels).