The article reviews the functions and regulation of RNA editing by adenosine deaminases acting on RNA (ADAR) enzymes, focusing on A→I RNA editing. A→I RNA editing, which converts adenosines to inosines in double-stranded RNA (dsRNA) substrates, is mediated by ADAR enzymes and can lead to codon changes and alterations in protein-coding sequences of certain genes. However, most A→I RNA editing sites are located in noncoding sequences, such as introns and 5' and 3' untranslated regions (UTRs). The biological significance of noncoding RNA editing remains largely unknown, but it has been proposed to play a role in controlling endogenous short interfering RNAs (esiRNAs) and regulating the biogenesis and functions of microRNAs (miRNAs). Recent studies have revealed that A→I RNA editing can modulate the processing of miRNA precursors and affect the selection of target genes for silencing by edited miRNAs. The review also discusses the domain structures of ADARs, their regulation, and the interaction between RNA editing and RNA interference (RNAi) pathways. Additionally, it explores the physiological consequences of RNA editing deficiencies and mutants with altered editing patterns, as well as the involvement of ADAR and inosine-containing RNAs in other functions.The article reviews the functions and regulation of RNA editing by adenosine deaminases acting on RNA (ADAR) enzymes, focusing on A→I RNA editing. A→I RNA editing, which converts adenosines to inosines in double-stranded RNA (dsRNA) substrates, is mediated by ADAR enzymes and can lead to codon changes and alterations in protein-coding sequences of certain genes. However, most A→I RNA editing sites are located in noncoding sequences, such as introns and 5' and 3' untranslated regions (UTRs). The biological significance of noncoding RNA editing remains largely unknown, but it has been proposed to play a role in controlling endogenous short interfering RNAs (esiRNAs) and regulating the biogenesis and functions of microRNAs (miRNAs). Recent studies have revealed that A→I RNA editing can modulate the processing of miRNA precursors and affect the selection of target genes for silencing by edited miRNAs. The review also discusses the domain structures of ADARs, their regulation, and the interaction between RNA editing and RNA interference (RNAi) pathways. Additionally, it explores the physiological consequences of RNA editing deficiencies and mutants with altered editing patterns, as well as the involvement of ADAR and inosine-containing RNAs in other functions.