The paper discusses the property of rolling resistance as applied to pneumatic tires. Reference is made to the low power source vehicles presently under development and the importance of providing a tire compatible with this type of vehicle. The emphasis is placed on minimizing the power consumption in tires and the relationship of this minimization to the other performance properties of the tire. Basic relationships of rolling resistance are discussed as associated with structural and environmental factors in both low and high speed operation. The discussion covers only tire service over hard surfaces and is primarily concerned with passenger car tires.