The liquid impact properties of a range of infra-red and optical transmitting materials have been investigated using the liquid jet impact technique. In particular the effects of temperature and pre-existing stress fields on the liquid impact performance of certain materials have been examined. Consideration of these aspects of liquid impact has been supplemented by measurements of related fracture properties. The correlation between liquid jet impact and liquid drop impact has been re-examined for normal impact by comparing impacts on perspex. This correlation has been extended to consider angled impact. Components that are subjected to liquid impact may simultaneously be subjected to elevated temperatures. A system has been developed to allow experimental investigation of the liquid impact performance of materials at elevated temperatures. Preliminary results were obtained on a polymer (PEEK). The amount of damage resulting from liquid impact increased with temperature. Subsequently two brittle materials (glass and zinc sulphide) were investigated. Thermal shock has been shown to be the dominant failure mechanism for these materials at temperatures of 300<SUP>o</SUP>C and greater. Pre-existing stresses in a material can affect not only its static but also its dynamic loading response. The liquid impact performance and some associated fracture properties of toughened glass systems have been investigated. Chemically and thermally toughened systems were compared. There is a small increase in the threshold velocity for the toughened glasses considered compared to soda-lime glass. The toughening stresses distributions led to differences in the behaviour under single and multiple impact. A novel computer simulation of liquid impact onto pre-stressed substrates has been developed. It is based on the interaction of a model Rayleigh surface wave with a flaw distribution. Good agreement with experiment was obtained for a thermal toughening stress distribution.