This paper presents the results of an experimental program to study size and geometry effects in CTOD R-curves. The results were obtained from room temperature unloading compliance R-curve tests on different-sized single-edge-notch-bend (SENB) specimens made from Ti-3Al-2.5V alloy, HY100 steel, and nickel-aluminum-bronze (NAB). The crack growth resistance was measured in terms of conventional CTOD, δ0 (i.e., as defined in BS 5762), CTOD corrected for crack growth, δR, and CTOD derived using a double clip gage arrangement, δdc. It was found that all the CTOD R-curves exhibited upswings after crack extensions corresponding to approximately 15% of the initial uncracked ligament. Based on the results obtained in this study, it is postulated that the crack growth limit for CTOD controlled crack growth in R-curves is 15% of the initial uncracked ligament. This condition alone, however, is not sufficient to guarantee size/geometry independent results. It is also necessary to have the same level of specimen constraint.