Nanoparticle-based therapeutics are poised to become a leading delivery strategy for cancer treatment because they potentially offer higher selectivity, reduced toxicity, longer clearance times, and increased efficacy compared to conventional systemic therapeutic approaches. This article reviews existing nanoparticle technologies and methods that are used to target drugs to treat cancer by altering signal transduction or modulating the tumor microenvironment. We also consider the implications of recent advances in the nanotherapeutics field for the future of cancer therapy.