Exosomes are extracellular vesicles with a diameter of about 30 to 100 nm, which play a crucial role in intercellular communication. Compared with normal cells, the release rate of tumor-derived exosomes (TDEs) significantly increased, and exosomal contents, especially microRNAs (miRNAs), greatly changed. TDEs contribute to the proliferation, metastasis and resistance of tumor cells, regulate immune response and tumor autophagy, and mediate tumor-stroma communication. In addition, exosomes may be involved in tumor complications. In view of the role of exosomes in intercellular communication, exosomes have been developed as tumor biomarkers, therapeutic targets, and drug delivery systems for tumor diagnosis, prognosis and treatment. Despite the many advantages of exosomes, there are many challenges in exosomal development and application, such as incomprehensive understanding of biological functions, safety and specificity for therapeutic use. This article reviews the biogenesis of TDEs and focuses on the role of exosomal miRNAs in intercellular communication and exosome-based treatment for cancer.