AbstractThree‐Phase fluidized bed bioreactors have advantages over conventional chemical reaction systems. There is a lack of agreement over most major operational conditions, and a wide range of design variables are open to question. A large body of recent work in the field has been reviewed, with a degree of historical comparison and discussion.It has been found that aspects of fluidized bed biofilm reactors of vital importance include: choice of solid media, gas and liquid loadings, bacterial type and reactor mechanical design. A large proportion of the work in the field of three‐phase fluidization is non‐biologically specific, or not tested on a bacterially inoculated system.The majority of three‐phase fluidized bed bioreactor work is in the field of water treatment. Although this work has highlighted the potential for use of bio‐fluidized beds for this application, there are still specific problems hindering the large scale industrial acceptance of three‐phase fluidized bed