The aim of this chapter is to discuss the flammability characteristics of nanocellulose-reinforced thermoset nanocomposites. The work presents the background on fire retardancy, thermoset polymers and cellulose, and nanocellulose materials. The strategies to impart flame retardancy into thermoset cellulose nanocomposites and their fire resistance performance have been discussed. The different characterization techniques used to measure the flammability and possible industrial applications of thermoset cellulose nanocomposites have also been enumerated.