The search for high stiffness, low density materials has led to the production of magnesium based metal matrix composites using a variety of particles and whiskers as reinforcements. Examples are silicon carbide particles and whiskers; boron carbide and boron particles. To date most of the techniques used to produce these composite materials have used powder metallurgy. This results in a very high cost product which is limited to wrought forms.Several companies have attempted to overcome these problems by developing alternative processing technologies. Magnesium Elektron Limited has developed a process which combines silicon carbide particles with magnesium alloys in the liquid state. The resultant material can be used either as a casting alloy or for extrusions and forgings. This composite has an increased stiffness of up to 30% and a significant increase in strength. By controlling the ceramic content of the composite the physical properties such as CTE can also be varied to suit the specific application.This paper will review the development of particulate reinforced magnesium alloys and discuss the properties of the material being produced at MEL.