Detailed investigations of microstructual evolution in multicomponent Al-Si eutectic alloys as a function of composition and cooling rate have been carried out. A variety of experimental techniques, including image analysis, optical and electron microscopy, have been used in conjunction with thermodynamic modelling to obtain an understanding of the volume fraction and distribution of phases within the microstructure as a function of chemical composition and process parameters. In particular, the effect of additions of Ti, Zr and V have been studied and their influence on the development of the microstructure, and hence mechanical properties, determined.