Extracellular vesicles (EVs) are nano-sized, membrane-enclosed structures secreted by various cell types, playing crucial roles in cellular communication and disease progression. EVs can transport proteins, mRNAs, miRNAs, DNA, and lipids, influencing physiological and pathological events, including tumor microenvironment (TME) dynamics. They are promising tools for therapeutic agents, drug delivery systems, and disease biomarkers, particularly in cancer diagnostics and targeted therapy. EVs are found in various body fluids and can be detected through liquid biopsies, offering non-invasive diagnostic potential. The review discusses the biogenesis, composition, and roles of EVs in various conditions, including cancers (head and neck, lung, gastric, breast, and hepatocellular carcinoma), neurodegenerative disorders, diabetes, viral infections, autoimmune and renal diseases. EVs are classified into exosomes, apoptotic blebs, and microvesicles, with specific subtypes like oncosomes and prostasomes. Their presence and behavior in these conditions highlight their potential in enhancing cancer management and other therapeutic applications. The review also explores the sources of EVs, such as stem cells and immune cells, and their roles in immune responses and pathogen interactions. Finally, it delves into the detailed mechanisms and molecular contents of EVs, emphasizing their significance in molecular diagnostics and therapeutics.Extracellular vesicles (EVs) are nano-sized, membrane-enclosed structures secreted by various cell types, playing crucial roles in cellular communication and disease progression. EVs can transport proteins, mRNAs, miRNAs, DNA, and lipids, influencing physiological and pathological events, including tumor microenvironment (TME) dynamics. They are promising tools for therapeutic agents, drug delivery systems, and disease biomarkers, particularly in cancer diagnostics and targeted therapy. EVs are found in various body fluids and can be detected through liquid biopsies, offering non-invasive diagnostic potential. The review discusses the biogenesis, composition, and roles of EVs in various conditions, including cancers (head and neck, lung, gastric, breast, and hepatocellular carcinoma), neurodegenerative disorders, diabetes, viral infections, autoimmune and renal diseases. EVs are classified into exosomes, apoptotic blebs, and microvesicles, with specific subtypes like oncosomes and prostasomes. Their presence and behavior in these conditions highlight their potential in enhancing cancer management and other therapeutic applications. The review also explores the sources of EVs, such as stem cells and immune cells, and their roles in immune responses and pathogen interactions. Finally, it delves into the detailed mechanisms and molecular contents of EVs, emphasizing their significance in molecular diagnostics and therapeutics.