This chapter provides a detailed assessment of two major groups of technical issues associated with the cofiring of coal and biomass in pulverised fuel boilers. These are: (i) combustion-related issues; and a brief overview of (ii) issues related to ash deposition. The emissions and ash disposal issues are dealt with separately in detail in Chapter 6. A series of examples is also presented in Chapter 8 to show the extent to which the technical issues discussed in Chapters 4-6 impact upon a cofiring operation and to demonstrate the most effective course of action to resolve these problems in a practical situation.