ncRNAs are important regulators of gene expression and critical for transcriptional regulation, although non-coding RNAs do not make proteins. ncRNAs were initially discovered in the 1960s together with rRNAs and tRNAs and are categorized as either lncRNAs (lncRNAs, >200 nucleotides) or sncRNAs (<200 nucleotides). The study of ncRNAs was expanded with the identification of snRNAs in the 1980s and microRNAs in the 1990s, which showed their capacity for regulation. Later developments in bioinformatics and high-throughput sequencing revealed the complexity and diversity of ncRNAs, such as cRNAs, snoRNAs, piRNAs, and siRNAs. Regulation of gene expression by ncRNAs is important and occurs through a number of mechanisms, such as RNA processing, transcriptional changes, chromatin remodeling, and epigenetic modification. MicroRNAs and short interfering RNAs, for instance, mainly control mRNA stability and translation, but long non-coding RNAs and circular RNAs are known to affect chromatin structure and transcription factor activity. The functions of ncRNAs in maintaining nuclear architecture, intercellular signaling, and epigenetic modifications have also been brought to light in recent years. The correlation of ncRNA with diseases like cancer and their potential use as therapeutic targets and diagnostic markers provide evidence of ncRNA clinical value in transcriptional regulation.