This work elucidates the fundamental concepts that are essential to understand fluidized bed agglomeration and reviews the development of tools used to predict it. The process of agglomeration in fluidized bed combustion and gasification systems has been explained, along with the associated mechanisms. The ash chemistry and particle physics that influence the agglomeration process have been reviewed to help choose the type of fuel and reactor configurations that can minimize the problem. The parameters that affect agglomeration and their interdependence have been reviewed in detail in order to understand the demands placed on detection, modeling, and prediction tools. Further, the current status of various prediction methods, their challenges, and avenues for further development have been identified. Insights into the development of comprehensive mathematical models to predict agglomerate growth kinetics have also been provided.