To reduce greenhouse gas emissions from fossil fuel fired power plants, a range of new combustion technologies are being developed or refined, including oxy-fuel combustion, co-firing biomass with coal and fluidized bed combustion. Flame characteristics under such combustion conditions are expected to be different from those in normal air fired combustion processes. Quantified flame characteristics such as temperature distribution, oscillation frequency, and ignition volume play an important part in the optimized design and operation of the environmentally friendly power generation systems. However, it is challenging to obtain such flame characteristics particularly through a three-dimensional and non-intrusive means. Various tomography methods have been proposed to visualize and characterize flames, including passive optical tomography, laser based tomography, and electrical tomography. This paper identifies the challenges in flame tomography and reviews existing techniques for the quantitative characterization of flames. Future trends in flame tomography for industrial applications are discussed.