The development of biomarkers for application in diagnostics, in the identification of resistance and virulence mechanisms and in breeding for disease resistance is well underway. Proteomics, transcriptomics, and genomics are the all-embracing tools to reach these goals, to compete the high complexity of regulation that complicates the search for suitable candidate genes and markers. Small RNA molecules, microRNA, visible since decades, however only recently discovered, add a new quality to the "omics"-family. Although still in the process of elucidation, they have been figured out as nucleic acids with outstanding impact on development and homoeostasis of cells and associated disorders. Their dysfunction that might be caused by endogenous and exogenous factors, can lead to developmental disorders, cancer, and also metabolic disorders, immunological disorders, and disease. Their role as a conductor in the orchestra of gene regulation and their stability and traceability in serum make them the ideal biomarkers. Deciphering of associations between miRNA and disease still have mainly been achieved in human medicine, however, miRNAs are on the way to be widely used in veterinary medicine and diagnostics too. This review presents an overview on the most significant findings, related to miRNA, including most comprehensive leading articles to deepen the topic.