The Gordon Research Conference (GRC) and Gordon Research Seminar (GRS) on CO2 Assimilation in Plants from Genome to Biome explores the dynamics of carbon exchange between the biosphere and the atmosphere from genome to biome scales. This area of active research is of critical importance to (1) predicting physiological and evolutionary responses of photosynthetic organisms to variable environments, (2) managing natural ecosystems for biodiversity, productivity, and carbon storage, and (3) promoting food and energy security for a growing world population. Photosynthesis research is an inherently interdisciplinary field, requiring basic scientific advances in many disciplines within plant, algae and microbial biology, coupled with efforts to integrate knowledge across molecular, cellular, organismal, and ecosystem scales. The subtheme for the 2021 GRC and GRS, "Photosynthetic Efficiency in a Changing Climate", encompasses these fundamental scientific problems. This theme was chosen to highlight scientific questions at the nexus of molecular, genomic, physiological, ecological, and evolutionary biology to encourage collaborative, innovative approaches to solving global challenges associated with climate change, carbon storage, and food and energy security. A major theme of the 2021 meeting will focus on obtaining a better understanding of how CO2 assimilation in plants will respond and can be enhanced under current and future climate change using historical adaptions to provide insights. The increase in atmospheric CO2 levels above 400 ppm, which over the long-term has resulted in increased global temperatures and extreme weather events, enhanced ocean acidification, will continue to influence CO2 assimilation in plants. Furthermore, the need for carbon-based fuels is skyrocketing along with increasing demand for food production in order to support an ever-increasing human population. The nexus between food and fuel demand is already having an impact on many societies on a global scale, and alterations in climate are exacerbating the problem. Multiple reports from the Intergovernmental Panel on Climate Change have highlighted the severity and urgency of these issues. As such, scientists have been presented with a grand challenge: determine how to more efficiently convert carbon into food and fuel before more conflict over them arises. To accomplish this, a second “green revolution” that surpasses the rate of current crop and fuel production is required and improving photosynthetic efficiency of CO2 assimilation in plants is central to this goal.