The article provides an overview of small silencing RNAs (ssRNAs), including microRNAs (miRNAs), small interfering RNAs (siRNAs), and Piwi-interacting RNAs (piRNAs). These ssRNAs play crucial roles in gene regulation and genome defense across various eukaryotic kingdoms. The biogenesis, function, and target regulation of each class of ssRNA are discussed, highlighting their distinct mechanisms and interconnected pathways. The article also explores the complex interactions between different ssRNA pathways, such as the competition and collaboration between siRNA and miRNA pathways. Additionally, it delves into the recent discoveries of new ssRNA classes, such as endo-siRNAs in plants, animals, and mammals, and the role of piRNAs in the germ line. The evolutionary origins and future directions of ssRNA research are also addressed, emphasizing the need for further investigation into the mechanisms and functions of these regulatory RNAs.The article provides an overview of small silencing RNAs (ssRNAs), including microRNAs (miRNAs), small interfering RNAs (siRNAs), and Piwi-interacting RNAs (piRNAs). These ssRNAs play crucial roles in gene regulation and genome defense across various eukaryotic kingdoms. The biogenesis, function, and target regulation of each class of ssRNA are discussed, highlighting their distinct mechanisms and interconnected pathways. The article also explores the complex interactions between different ssRNA pathways, such as the competition and collaboration between siRNA and miRNA pathways. Additionally, it delves into the recent discoveries of new ssRNA classes, such as endo-siRNAs in plants, animals, and mammals, and the role of piRNAs in the germ line. The evolutionary origins and future directions of ssRNA research are also addressed, emphasizing the need for further investigation into the mechanisms and functions of these regulatory RNAs.