If concrete science and technology are to keep pace with developments in other fields of engineering, it is essential that we make the most effective use of concrete materials. It is necessary to move beyond simply knowing the properties of the aggregates to an understanding and application of the effects of their properties on concrete in its various forms. The link between aggregate properties and performance in concrete is not yet entirely understood in many respects. Aggregate properties have profound influences on concrete properties, and these influences need to be understood and appreciated.