**Abstract**

Extracellular vesicles refer to exosomes, apoptotic bodies, microvesicles and large oncosomes, which are membrane bound structures secreted by cells including cancer cells. The pathological role and translational potential of extracellular vesicles (EVs) in cancers are receiving research attention recently. The cargoes of cancer-derived EVs retain the molecular properties of their sources and cancer cells actively release EVs into body fluids that are easy to access. EVs released from cancer cells not only promote cancer progression through the delivery of cancer-associated molecules but also reflect alterations in the state of cancers during therapy. They are considered promising biomarkers for therapeutic response evaluation, especially resistance to therapy and diagnostics. This chapter discusses the various roles of extracellular vesicles in cancers and their potential as therapeutic targets.

**Keywords:** extracellular vesicles, biomarkers, cancers, therapeutics
