One essential prerequisite for achieving design throughput and product conversion yield of cellulosic biofuel in commercial operation is a robust biomass feedstock preprocessing system. Such a system will reliably and steadily supply consistent quality feedstock to the conversion reactor. Pioneer cellulosic biofuel plants have encountered many feedstock handling challenges which lead to lengthy startup and difficulties in meeting plant nameplate production rate. Most of the biomass material handling challenges are caused by: (1) variability in biomass properties especially for herbaceous materials such as corn stover, (2) inadequate integrated testing of equipment, (3) not using the appropriate equipment or equipment design for the job, (4) mismatching of equipment capacity and turn down ratio, (5) lack of integrated control for the whole feedstock preprocessing system, and (6) inadequate surge capacity. This presentation will discuss the feedstock preprocessing challenges, identify key areas from equipment design and operation to process integration requiring optimization or further development to achieve robust integrated biomass feedstock preprocessing systems.