The present state of knowledge on the use of recycled concrete as an aggregate in new concrete is reviewed and suggestions made as to what further work is necessary before a proper assessment of the material can be made. Where crushed uncontaminated concrete is used the properties of the material as an aggregate and the basic engineering characteristics of the concrete made with it are well established. Much less is known about the type and quantity of impurities which could occur in crushed concrete from general building rubble and the effect these would have on concrete made using such crushed concrete as aggregate.