As a result of the advent of PSII driven oxygenic photosynthesis some 3 billion years ago, O2 rose in the atmosphere and CO2 fell. This atmospheric scenario presented the primary CO2 fixing enzyme Rubisco with an opportunity to become the dominant autotrophic carboxylase in an oxygen rich atmosphere but simultaneously presented it with problems due to its indiscriminate ability to fix both O2 and CO2 and its relatively low affinity for CO2. A common solution to Rubisco’s kinetic problems has been to develop photosynthetic CO2 concentrating mechanisms (CCMs) which turbocharge the enzyme with CO2. Cyanobacteria have done a particularly good job of this enabling CO2 to be concentrated up to 1000 fold compared to the external environment. The cyanobacterial CCM is based on a number of HCO3- and CO2 transport systems which accumulate HCO3- in the cytosol. This HCO3- is then used by Rubisco containing protein microcompartments within the cell to elevate CO2 around Rubsico’s active site. This talk will describe what we know about the cyanobacterial CCM and the efforts we are taking to introduce both HCO3- transporters and carboxysomes into plant chloroplasts to enhance the photosynthetic efficiency of C3 photosynthesis.