In recent years there has been a trend toward operating asphalt plants at lower mixing temperatures. These lower temperatures result primarily from a desire to conserve the energy required to produce the mixtures. The most direct result of lower mixing temperatures is lower temperatures during compaction. The effect of these lower compaction temperatures on performance has not been established, but laboratory studies have led to some questions that need to be addressed. The purpose of this paper is to summarize the results of a field and laboratory study performed at The University of Texas at Austin, Center for Transportation Research, to analyze the effect of lower compaction temperatures on the engineering properties of asphalt concrete mixtures.