Exosomes are membrane-bound nanovesicles containing lipids, proteins, and nucleic acids, secreted by nearly all cell types under physiological and pathological conditions. They facilitate intercellular communication by transferring biological signals between cells and are involved in both physiological and pathological processes. Exosomes can be used as biomarkers, vaccines, and drug delivery vehicles. However, accurately identifying, isolating, and quantifying exosomes remains a challenge. Exosome theranostics refers to their use in clinical diagnostics and therapeutic strategies. This review discusses the formation, uptake, and isolation of exosomes, their composition, and their roles in physiological and pathological processes. Exosomes contain various molecules, including proteins, lipids, mRNA, miRNA, and other non-coding RNAs. They play important roles in immune responses, neural communication, reproduction, and development. Exosomes can be used as biomarkers for disease diagnosis, including cancer, and as therapeutic agents in cancer immunotherapy and drug delivery. Exosomes can be engineered to enhance their therapeutic potential. Exosome theranostics has significant implications for translational medicine, offering new avenues for the development of effective clinical diagnostics and therapeutic strategies.Exosomes are membrane-bound nanovesicles containing lipids, proteins, and nucleic acids, secreted by nearly all cell types under physiological and pathological conditions. They facilitate intercellular communication by transferring biological signals between cells and are involved in both physiological and pathological processes. Exosomes can be used as biomarkers, vaccines, and drug delivery vehicles. However, accurately identifying, isolating, and quantifying exosomes remains a challenge. Exosome theranostics refers to their use in clinical diagnostics and therapeutic strategies. This review discusses the formation, uptake, and isolation of exosomes, their composition, and their roles in physiological and pathological processes. Exosomes contain various molecules, including proteins, lipids, mRNA, miRNA, and other non-coding RNAs. They play important roles in immune responses, neural communication, reproduction, and development. Exosomes can be used as biomarkers for disease diagnosis, including cancer, and as therapeutic agents in cancer immunotherapy and drug delivery. Exosomes can be engineered to enhance their therapeutic potential. Exosome theranostics has significant implications for translational medicine, offering new avenues for the development of effective clinical diagnostics and therapeutic strategies.