Cement is an essential constituent for the production of concrete. Nowadays, the supplementary use of cement such as industrial by-product and agricultural waste material has become an integral part of concrete construction due to their cost effective and sustainable environmental benefits. The industrial (metallurgical) by product-Granulated Blast Furnace Slag (GBFS) contains a non-crystalline silicon dioxide with high specific surface area and high pozzolanic reactivity. The use of GBFS either in cement or concrete has been increased due to its better performance in concrete in terms of strength and durability. In this paper, a critical review on the influence of slag and slag cement on the strength of sustainable concrete has been presented. The researches carried out in the past on the use of GBFS as partial replacement of cement in mortar and concrete, basically, the strength development of GBFS blended concrete and cement are reviewed in this study. These test results confirmed that the strength of cement mortar and concrete is varied with percent of slag replacement, fineness of slag and cement used, curing temperature as well as curing method. Based on the information available in literature, slag and slag cement could be a valuable material for the production of sustainable concrete.