RNA editing by ADAR deaminases converts adenosine to inosine (A→I) in double-stranded RNA (dsRNA), primarily affecting noncoding sequences in introns and untranslated regions. This process is mediated by ADAR enzymes, which are conserved across species. ADARs include ADAR1, ADAR2, and ADAR3, with ADAR1 and ADAR2 being more widely expressed. ADAR1 and ADAR2 are involved in both protein-coding and noncoding RNA editing, influencing gene expression and RNA interference (RNAi) pathways. A→I editing can alter protein functions by changing codons, leading to diverse protein isoforms. However, most A→I editing occurs in noncoding regions, potentially regulating RNAi and microRNA (miRNA) processing. ADARs are localized in the cytoplasm and nucleus, with ADAR1p150 primarily in the cytoplasm and ADAR1p110 in the nucleolus. ADAR1 is regulated by miRNA, and its expression is crucial for heart development. ADAR2 is involved in neuronal function and is essential for survival. Mutations in ADAR genes lead to various phenotypes, including neurodegeneration and metabolic disorders. A→I editing of miRNAs can affect their processing and function, influencing gene expression. Editing of pri-miRNAs can inhibit Drosha and Dicer cleavage, altering miRNA maturation. A→I editing of miR-376 cluster transcripts can redirect silencing targets, affecting gene expression in a tissue-specific manner. Overall, A→I RNA editing plays a critical role in regulating gene expression, RNAi, and miRNA function, with implications for human diseases and development.RNA editing by ADAR deaminases converts adenosine to inosine (A→I) in double-stranded RNA (dsRNA), primarily affecting noncoding sequences in introns and untranslated regions. This process is mediated by ADAR enzymes, which are conserved across species. ADARs include ADAR1, ADAR2, and ADAR3, with ADAR1 and ADAR2 being more widely expressed. ADAR1 and ADAR2 are involved in both protein-coding and noncoding RNA editing, influencing gene expression and RNA interference (RNAi) pathways. A→I editing can alter protein functions by changing codons, leading to diverse protein isoforms. However, most A→I editing occurs in noncoding regions, potentially regulating RNAi and microRNA (miRNA) processing. ADARs are localized in the cytoplasm and nucleus, with ADAR1p150 primarily in the cytoplasm and ADAR1p110 in the nucleolus. ADAR1 is regulated by miRNA, and its expression is crucial for heart development. ADAR2 is involved in neuronal function and is essential for survival. Mutations in ADAR genes lead to various phenotypes, including neurodegeneration and metabolic disorders. A→I editing of miRNAs can affect their processing and function, influencing gene expression. Editing of pri-miRNAs can inhibit Drosha and Dicer cleavage, altering miRNA maturation. A→I editing of miR-376 cluster transcripts can redirect silencing targets, affecting gene expression in a tissue-specific manner. Overall, A→I RNA editing plays a critical role in regulating gene expression, RNAi, and miRNA function, with implications for human diseases and development.