Moire interferometry is employed to study toughening in two classes of ceramic materials, nominally pure alumina and partially stabilized zirconia (PSZ). Energy to fracture as a function of crack growth curves (R curves) are derived from mode I compliance calculations and from near tip fitting of the moire fringes to linear elastic fracture mechanics (LEFM) asymptotic displacement fields. The effect of shielding by crack bridging in the alumina and by phase transformation in the zirconia is found by comparing the bulk compliance R curves to the locally derived morie R curve. Localized strain field plots are produced from the moire data for the PSZ zirconia. The observed transformation zone height compares favorably with that predicted by Okada et al. (1991), as does the qualitative nature of the R curve with predictions by Stump et al. (1988).