A major stream of post-consumer plastics is a commingled blend of polyethylenes and polypropylenes, which usually exhibits lower performance compared with that of the homopolymers due to the incompatible nature of polyethylenes and polypropylenes. Various studies have been carried out to characterize the structure, morphology, mechanical, thermal, and theological behavior of this blend. The effect of processing, modification, and compatibilization have also been studied by various workers. This article is a review of the work done on polyethylene-polypropylene blends to help in the understanding of this important blend.