The need for reinforcements in structural ceramicmatrix composites to be used in air at temperatures above 1000 8C has encouraged great changes in smalldiameter ceramic fibres since their initial development as refractory insulation. There now exists a range of oxide and non-oxide fibres with diameters in the range 10-20mm which are candidates as reinforcements [1]. Applications envisaged are in gas turbines (both aeronautical and ground based), heat exchangers, first containment walls for fusion reactors as well as uses for which no matrix is necessary such as candle filters for high-temperature gas filtration. Applications in industrial gas turbines are discussed in chapter 5, and other applications are described in chapters 16 and 17.