The fracture surfaces of HY-100 steel and 2024 aluminum tensile specimens with differing gage lengths and gage diameters were examined using scanning electron microscopy. Relationships were found between various fractographic features and the toughnesses of the specimens as quantified by the global critical strain energy density, wc, which is a measure of the work necessary to fail a material specimen by monotonic loading. In both test materials, correlations were made between the percentage of the fracture surface characterized by a particular fracture mode and the toughness of a given specimen. Correlations could also be made between the toughness of a specimen and other fractographic features such as the linear microvoid density or the aspect ratio of microvoids. It was found that both the character of the fracture surfaces and the specimen toughnesses were dependent on the history of the triaxiality of the stress-strain state which in turn was dependent on the gage geometries of the specimens. These results indicate that quantitative interrelationships between the micromechanical behavior and the global response of a specimen may be derived through the concepts employed in this investigation.