Some physical properties of magnesium are reviewed. A discussion of the corrosion mechanisms at work on magnesium under various environmental conditions follows. The role of base metal impurities is investigated. The strengths and limitations of the more traditional corrosion protection methods are discussed. Several modern non-paint surface treatments and still largely experimental corrosion resistant surface modification techniques are assessed. Magnesium based composites are of special interest, in particular the magnesium-graphite fiber composite system. The latter has been identified as unique for certain space satellite applications by virtue of its very favorable physical properties. Its principal drawback, susceptibility to severe corrosion in most environments, is discussed. Some consideration is devoted to preserving the desirable properties of Gr-Mg composites while incorporating interface modification or substitute reinforcement materials. Finally, recommendations are made for successfulab initio design of corrosion protection into magnesium based components in light or recent research developments.