A number of examples exist that indicate the potential for increasing the toughness of brittle. matrices by dispersing different reinforcements. For further development of these advanced materials the actual material response during mechanical loading under presence of flaws appears to be important. Theoretical and experimental knowledge acquired on different kinds of brittle matrix composites is summarised in the paper. These include glass matrix composites with metallic particles, alumina platelets, continuous SiC (Nicalon (R)) fibres, and both chopped fibres and ZrO2 particles (hybrid composites). The composites were tested in as-received state but also after different forms of thermomechanical loading, e.g. thermal shock, thermal cycling in air, which were investigated according to the envisaged composites application. Chevron notch technique was mainly used for fracture toughness evaluation. Microstructural damage is explained based on identified fracture micromechanisms.