This chapter examines in detail the main cofiring issues associated with biomass fuel preparation, storage and handling, as well as blend ratios and milling processes. The findings of previous studies in cofiring and milling are reported and, in particular, the methods, techniques and results of recent CCSD experimental milling studies are discussed. How biomass fuel factors contribute to other technical issues associated with co-combustion and ash deposition and disposal is also addressed in Chapters 5 and 6, with practical applications described in case studies in Chapter 8.