Aquatic photosynthetic organisms, including the green alga, Chlamydomonas reinhardtii , induce a set of genes for a carbon concentrating mechanism (CCM) through the CO2-signalling system, to acclimate to CO2-limiting stress conditions. We have described a regulatory gene, Ccm1 , which was shown to regulate CCM induction in C. reinhardtii . In this review, we summarize the current understanding of the regulatory process, which controls the expression of genes for the CCM. In particular, CCM1-regulated genes and possible functions of Ccm1 in the CO2-signalling pathway are discussed, in relation to findings in other green algae and cyanobacteria.