The geometric and crystallographic characteristics of interfaces in WC-Co composites with a range of grain sizes and carbide volume fractions have been comprehensively characterized. The carbide crystals are most frequently terminated by (0001) and (10 (1) over bar0) surfaces. The average number of carbide vertices per grain and the basal-to-prismatic face area ratio of the WC-Co interfaces increase with the carbide volume fraction. The three most frequently occurring WC/WC grain boundaries are 901 twist boundaries about [10 (1) over bar0], 30 degrees twist boundaries about [ 0001], and asymmetric 90 degrees boundaries about [(2) over bar 110]. The boundary populations do not vary with grain size or carbide volume fraction, suggesting that they are determined by the grain boundary energy anisotropy.