Many aquatic photosynthetic microorganisms possess inducible CO2 concentrating mechanisms (CCMs) that allow them to optimize carbon acquisition in environments with frequently changing and often limiting CO2 concentrations. The CCMs function by accumulation of a large quantity of intracellular inorganic carbon (Ci) through concerted Ci uptake systems and enzymes catalyzing the interconversion between different species of Ci. In addition, an array of regulatory devices appears present to facilitate the sensing of CO2 availability and the regulation of metabolic pathways. Over the past several decades, significant advances have been made in understanding the CCM and its regulation. With the aid of mutant studies and the availability of several cyanobacterial and eukaryotic algal genomes, an integrated picture is emerging to reveal many of the molecular details in the microalgal CCMs. This review will focus on the recent advances in identifying and characterizing the major components involved in the CCM, including Ci uptake systems and regulatory pathways in eukaryotic microalgae, especially in the model organism, Chlamydomonas reinhardtii.