Biofilms are defined as microbial cell layers, which are irreversibly or reversibly attached on solid surfaces. These attached cells are embedded in a self-produced exopolysaccharide matrix, and exhibit different growth and bioactivity compared with suspended cells. With their high biomass density, stability, and potential for long-term fermentation, biofilm reactors are employed for the fermentation and bioconversion, which need large amount of biomass. During the past decade, biofilm reactors have been successfully applied for production of many value-added products. This review article summarizes the applications of biofilm reactors with different novel designs. Advantages and concerns using biofilm reactors, potential uses for industrial-scale production, and further investigation needs are discussed.