In this chapter, we provide an overview of poly(ethylene glycol) (PEG)-tethered (PEGylated) polymer micelles and their application for anticancer drug delivery carrier. An amphiphilic block copolymer forms a core-shell type of polymeric micelle in aqueous media that can be utilised as a carrier for the delivery of hydrophobic drugs. The incorporation of anticancer drugs into the core of PEGylated polymer micelles increases the solubility, stability and circulation of the drugs. Recently, new types of polymeric micelles have been proposed, including micelles characterised by pH-triggered disintegration and formation of a polyion complex of hydrophilic block polymers. For example, pH-sensitive PEGylated polymer micelles can control drug release and have been shown to be an effective chemotherapy with enhanced therapeutic efficacy against cancer cells. Therefore, PEGylated polymer micelles should perform well as a carrier for anticancer drug delivery.