Microstructural evolution during thermomechanical processing of a Fe-Mn-Co-Cr-Si-Cu high entropy alloy (HEA) was studied to compare the effect of friction stir processing (FSP) with cold rolling. The difference in microstructural evolution in the two routes was evaluated. A thorough annealing study of the FSP and rolled specimens illustrated the propensity of phase, grain and twin evolution, and quantified the same. Recrystallization behavior during annealing was determined to be dependent on prior processing as well as annealing route. Single-step annealing of FSP specimens and two-step annealing of FSP and rolled specimens yielded similar microstructural evolution with increasing annealing time. However, single-step annealing of rolled specimens led to entirely different microstructural evolution. A detailed study revealed that various interdependent and competing phenomena such as phase transformation, precipitation, recovery, recrystallization and grain growth and twinning are responsible for the overall microstructural evolution. Some unique mechanisms of annealing twin formation that were observed included formation of a twin at the interface of an epsilon (hexagonal close packed) martensite plate with the gamma (face centered cubic) parent grain and at a grain boundary triple junction containing a precipitate. © 2019 Acta Materialia Inc.