Part I: General features and technical issues related to circulating microRNA -- 1. Introduction to microRNAs: biogenesis, action, relevance of tissue microRNAs in disease pathogenesis, diagnosis and therapy. The concept of circulating microRNAs -- 2. Extracellular microRNAs in membrane vesicles and non-vesicular carriers -- 3. Technical aspects related to the analysis of circulating microRNAs -- Part II: Diagnostic relevance of circulating microRNAs -- 4. Circulating blood-borne microRNAs as biomarkers in solid tumors -- 5. Circulating microRNA as biomarkers in hematological malignancies -- 6 Circulating microRNAs as biomarkers in cardiovascular diseases -- 7 Circulating microRNAs in neurodegenerative diseases -- 8 Circulating extracellular microRNA in systemic autoimmunity -- 9. Circulating microRNAs in inflammatory bowel diseases -- 10. Circulating microRNAs in diabetes progression: discovery, validation and research translation -- 11. Diagnostic relevance of microRNAs in other body fluids including urine, feces and saliva -- Part III: Potential biological relevance of circulating microRNA -- 12 Circulating microRNAs as hormones - intercellular and inter-organ conveyors of epigenetic information? -- 13. Are circulating microRNAs involved in tumor surveillance? -- 14.-Hypothetic interindividual and interspecies relevance of microRNAs released in body fluids.