"Cement content, water-to-cement ratio (w/c), aggregate size and type, specimen size and shape, loading rate, and curing are some factors that affect the concrete compressive strength. This study focuses on the effect of aggregate type and specimen configuration on the compressive strength of concrete. Six concrete mixes utilizing 10 mm and 20 mm natural, LAYTAG and Pumice lightweight, and recycled aggregate from two sources, “Bee’ah and Jabal Ali”, were used to investigate the effect of these two factors. In addition, samples from ready-mix concrete producers with different strengths “C45, C75, C60, and C80” were evaluated for the compressive strength using standard size cylinders and cubes. Strength development was monitored on the 7th, 28th, and 90th day. In addition, flexural strength, split tension, and modulus of elasticity were evaluated on the 28th and 90th day. Statistical analyses were conducted to estimate the relationships among the variables considered in the investigation. Moreover, other mechanical properties as a function of compressive strength were discussed and compared to those predicated by the ACI specification. Results indicate that standard specimen size has a negligible effect on the concrete compressive strength; whereas, specimen shape had a noticeable effect on the compressive strength as the Cylinder/Cube ratio on the 90th day was ranging between 0.781 and 0.929. The concrete compressive strength and modulus of elasticity were significantly affected by the aggregate type. Other mechanical properties, such as flexural strength and split tensile strength, were less affected by the aggregate type which was also confirmed by the values predicted with the ACI equations."--Abstract.