An overview of the effect of partial replacement of traditional hydraulic binders in concrete by metakaolin is presented. Metakaolin is an artificial pozzolan obtained by the calcination of kaolinitic clays over a specific temperature range. The use of metakaolin as a pozzolanic addition in partial substitution of cement in concrete has seen an increasing interest in the last decade. In general, an overall improvement of concrete properties can be obtained by the use of metakaolin in concrete. The most important benefits are related to the improvement of concrete compressive strength and the increase of concrete durability. The latter is achieved through reduction of chloride penetration poten- tial and also through reduction of expansive reactions in concrete. A more sustainable concrete can also be achieved with the use of metakaolin.