Fluidized beds are commonly found in the chemical and energy processing industries because of their low pressure drop, uniform temperature distribution, and high heat transfer rates. For example, in biomass gasification, biomass particles are injected into a heated bubbling bed of inert material (typically refractory sand) that volatilizes to form a flammable gas. However, the movement of the biomass particle through the bubbling bed is difficult to quantify because the systems are opaque. This paper describes X-ray particle tracking velocimetry (XPTV) applied to fluidized beds, where X-ray flow visualization is used to track the location of a single fabricated tracer particle as a function of time in a fluidized bed to study the bed/particle hydrodynamics. Using stereoscopic X-ray imaging, the 3D position of the tracer particle as a function of time is determined, from which tracer particle velocity can be calculated. Details and challenges of the XPTV process are also summarized.