Acoustic emission (AE) is an attractive technique for the structural health monitoring (SHM) of aerospace systems. To reach its full potential in this role a quantitative approach must be adopted to study damage mechanisms in composite materials. In this paper, some of the practical issues regarding acoustic emission testing in composites are addressed. A model describing Lamb wave propagation through plates is described and used to make phase velocity and attenuation measurements in both aluminium and carbon fibre reinforced plastic plates. Results are then implemented in the frequency domain to conduct an experimental study of normal incidence Lamb wave reflections. Comparisons are made with finite element analysis (FEA) models with good results.