Reliable design of ceramic matrix composite components in aerospace applications requires the knowledge of the crack propagation behavior of these materials at elevated temperatures. The first part of this paper discusses a test setup using a centrally notched disk to conduct mechanical fatigue crack growth testing of brittle matrices used in these composites. The specimen compliance is monitored using the laser interferometric displacement gage system. To evaluate this fatigue crack growth test setup, cyclic crack propagation is studied in an alumina ceramic specimen. Transmission electron microscopy of surface replicates show evidence of irreversible microcracking at the crack tip that could provide the mechanism for fatigue crack growth in this ceramic. The second part of this paper discusses the results from automated fatigue crack growth tests on silicon-carbide fiber-reinforced aluminosilicate glass matrix composites at room and elevated temperatures using the compact tension geometry. Tests conducted at room temperature indicate high damage tolerance in these composites due to energy dissipation through distributed matrix cracking around the tip, fiber bridging, and fiber pull out. In contrast, tests at 650°C reveal Mode 1 self-similar crack growth in these composites and absence of fiber pullout.