Whole-genome sequencing analyses revealed that the majority of the human genome is transcribed and identified thousands of protein non-coding transcripts. Non-coding RNAs (ncRNAs) are divided into two main groups: small and long ncRNAs. This review is focused on the regulatory ncRNAs mainly on microRNAs and long ncRNAs. These ncRNAs regulate gene expression at the transcriptional and post-transcriptional levels. In this context, ncRNAs are involved in the regulation of most cellular processes and their deregulation has serious impacts on the phenotype. Hundreds of studies have implicated ncRNAs in the pathogenesis of many diseases ranging from metabolic disorders to diseases of organ systems as well as various types of cancers.Clinically, ncRNAs belong to a new generation of diagnostic and prognostic biomarkers with a great potential. Due to high tissue specificity and ability to regulate multiple genes often within one signaling pathway, ncRNAs represent attractive therapeutic targets. Increasing knowledge about a wide spectrum of ncRNA actions demonstrate a pivotal role of these transcripts in expression regulation. Many aspects of the ncRNA biology are still unclear and their understanding will provide us a new perspective on the complexity of the regulatory network.