Mixed micelles self-assembled from two or more dissimilar block copolymers provide a direct and convenient approach to improved drug delivery. The present review is focused on mixed micelles (prepared from block copolymers only) for various drug delivery applications along with their merits over single-copolymer micelles. Presented are the physicochemical properties of mixed and single-copolymer micelles, various stimuli-responsive mixed micelles for the treatment of cancer, interesting combinations of multifunctional mixed micelles along with their in vitro and in vivo performance, and the potential of mixed micelles as a gene delivery system. Finally, the performance of mixed micelles in preclinical and clinical testing is explained. In addition, the interaction of mixed micelles with cancer cells and the biosafety of mixed micelles are summarized. The in vitro and in vivo performance presented here clearly reveals that the mixed-micelle approach has a wider scope than that of the single-copolymer micelle approach and directs researchers to focus on this approach to delivery of drugs/gene/biologics for various applications.