The development of global microstructure characteristics has been compared to the local distribution and extent of Σ3 and Σ3n (1 n 3) grain boundary clusters as a function of thermo-mechanical processing in Type 304 stainless steel. A cold reduction of 5% produced GBE modified microstructures on annealing at 1050°C, containing almost one order of magnitude longer maximum cluster lengths than the corresponding annealing treatments for a reduction of 15%. Differences in the development of the distributions of cluster length scales were observed between the thermo-mechanical treatments. A re-conversion of the longest cluster obtained after GBE processing was observed with long annealing times. The local distribution of Σ3n boundary clusters was assessed, and regions with a low density of clusters are indicative of the onset of GBE conversion of microstructure.