This chapter explores recent reports of tomographic imaging of bubble column and fixed bed reactors. A brief introduction to these reactors is given, followed by a summary of some of the studies of these reactors using radioactive particle tracking, magnetic resonance imaging, wire mesh sensors, and X-ray, γ-ray, electrical capacitance, and electrical resistance tomography. This chapter concludes with an outlook for the future including a discussion of how these techniques will be used to develop computational modeling techniques for the characterization of these reactors, and how additive manufacturing (including 3D printing) will influence the design of these reactors.