Microalgae present one of the few technologies for the capture and utilization of CO2 emitted by power plants, These microscopic plants would be grown in large open ponds, into which power plant flue gas or pure CO2 (captured from power plants) is sparged, and, after harvesting, the biomass would be converted to a fossil fuel replacement, preferably a high value liquid fuel such as biodiesel. The requirements for large areas of land, favorable climate, and ample water supplies will restrict the potential of this technology. Also, even with rather favorable technical assumptions, the currently projected costs of microalgae-fuels are high, similar to most power plant CO2 capture and disposal options. However, if the technology of microalgae could achieve very high productivities, equivalent to 10% solar energy conversion, and if projected low-cost cultivation, harvesting and processing techniques could be developed, microalgae technology could become a low-cost CO2 mitigation option, particularly if prices for fossil fuels increase in the future. In the nearer-term microalgae CO2 utilization can be integrated with wastewater treatment and reclamation, providing an early application of this technology. Long-term basic and applied R&D are required to develop this technology, as one of the many options that may be required in the future to help preserve our planetary atmosphere and biosphere.