Exosome-derived microRNAs (Exo-miRNAs) have emerged as key signalling molecules in cancer progression, serving as a key link between mechanistic understanding and translational applications. These miRNAs, encapsulated within exosomes, are functionally active and play instrumental roles in various cancer hallmarks, including cell proliferation, immune evasion, angiogenesis, EMT, and metastasis. Compared to their free counterparts in blood, saliva, urine, and CSF, Exo-miRNAs exhibit enhanced stability, making them promising non-invasive biomarkers. Their cancer-specific expression patterns have been documented across multiple tumour types such as lung, breast, colorectal, brain, and prostate cancers. Moreover, alterations in exo-miRNA levels have been correlated with drug resistance, as validated by in vitro and in vivo functional studies. Therefore, clinically, exo-miRNAs have shown potential in differentiating between healthy and cancerous states, metastatic versus non-metastatic tumours, and drug-resistant versus responsive cases and are even associated with patient survival outcomes. Despite their promise, gaps remain in understanding their comprehensive functional roles, particularly in integrating diagnostic and prognostic value. This chapter provides a comprehensive overview of exo-miRNAs in cancer from their roles in tumour progression to their clinical utility. Furthermore, we highlight the synergistic value of combining exo-miRNAs with traditional biomarkers like cfDNA, CTCs, and protein markers to enhance diagnostic sensitivity and specificity.