MicroRNAs (miRNAs) are a class of highly evolutionarily conserved non-coding RNAs (ncRNAs) that modulate gene expression. Several studies have shown that the expression of miRNAs is deregulated in human malignancies. For ncRNAs and miRNAs, such gene-profiling studies in tumorigenic tissues have identified significant signatures that are of both diagnostic and prognostic value. Addressing the functions of ncRNAs not only give insights into the molecular mechanisms that underlie complex genetic processes, but may also elucidate novel mechanisms that contribute to early stages of tumor development, progression and metastasis. MiRNA-based novel approaches target the ncRNAome, including, for instance, miRNA expression levels and improved designs of miRNA-mimics or more precise target-predictions, prevent off-target effects of novel drugs and make miRNAs become a highly efficient class of therapeutics. For miRNA-based therapeutic studies two direct strategies are currently under investigation, viz. (i) the overexpression of given miRNAs to inhibit the expression of protein-coding genes or (ii) the inhibition of target miRNAs with antisense constructs like antagomiRs. Indirect strategies include the use of novel drugs that modulate miRNA expression levels by directly targeting their processing or transcription. Further, miRNA-based biomarkers have a significant impact on the development of both therapeutic and diagnostic agents, a concept known as theranostics and are highly relevant for drug development and personalized medicine.