Small silencing RNAs, including microRNAs (miRNAs), small interfering RNAs (siRNAs), and Piwi-interacting RNAs (piRNAs), have been identified since 1993. These RNAs differ in biogenesis, target regulation, and biological functions, yet they are interconnected and often compete or collaborate in gene regulation and genome protection. siRNAs are derived from double-stranded RNA (dsRNA) and are processed by Dicer into 21-24 nt duplexes, with one strand guiding RISC to cleave target mRNAs. In mammals, Dicer produces both miRNAs and siRNAs, while in Drosophila, Dcr-1 and Dcr-2 have distinct roles. siRNAs are involved in RNA interference (RNAi), which is systemic in plants and nematodes and can be heritable. siRNAs are also produced from endogenous sources, such as transposons and repetitive elements, and are involved in heterochromatin formation and transposon silencing. In plants, endogenous siRNAs (endo-siRNAs) are produced from transposons, repetitive elements, and tandem repeats, and are involved in gene regulation and chromatin modification. Trans-acting siRNAs (tasiRNAs) are generated by the interaction of miRNA and siRNA pathways. Natural antisense transcript-derived siRNAs (natsiRNAs) are produced in response to stress and regulate gene expression. Long siRNAs (lsiRNAs) are also produced in plants and are stress-induced. In animals, endo-siRNAs are produced from transposons, heterochromatic sequences, and mRNAs, and are involved in transposon silencing. In flies and mammals, endo-siRNAs are 21 nt long and are produced by Dicer. They are involved in maintaining germ line stability and fertility. In mice, endo-siRNAs are produced from transposons and are involved in DNA methylation. miRNAs are derived from precursor transcripts and are processed by Drosha and Dicer into 21-24 nt duplexes. They regulate gene expression by binding to complementary sites in mRNA 3' UTRs, often repressing translation or inducing cleavage. miRNAs are involved in diverse cellular pathways and are crucial for development and disease. piRNAs are the longest small RNAs and are involved in germ line development, particularly in silencing transposons. piRNAs are produced from long, single-stranded precursor RNAs and are involved in maintaining germ line stability and fertility. Small RNA pathways are interconnected and interact at multiple levels, competing for substrates and effector proteins. They are involved in gene regulation, transposon silencing, and genome protection. The study of small RNAs has revealed their roles in variousSmall silencing RNAs, including microRNAs (miRNAs), small interfering RNAs (siRNAs), and Piwi-interacting RNAs (piRNAs), have been identified since 1993. These RNAs differ in biogenesis, target regulation, and biological functions, yet they are interconnected and often compete or collaborate in gene regulation and genome protection. siRNAs are derived from double-stranded RNA (dsRNA) and are processed by Dicer into 21-24 nt duplexes, with one strand guiding RISC to cleave target mRNAs. In mammals, Dicer produces both miRNAs and siRNAs, while in Drosophila, Dcr-1 and Dcr-2 have distinct roles. siRNAs are involved in RNA interference (RNAi), which is systemic in plants and nematodes and can be heritable. siRNAs are also produced from endogenous sources, such as transposons and repetitive elements, and are involved in heterochromatin formation and transposon silencing. In plants, endogenous siRNAs (endo-siRNAs) are produced from transposons, repetitive elements, and tandem repeats, and are involved in gene regulation and chromatin modification. Trans-acting siRNAs (tasiRNAs) are generated by the interaction of miRNA and siRNA pathways. Natural antisense transcript-derived siRNAs (natsiRNAs) are produced in response to stress and regulate gene expression. Long siRNAs (lsiRNAs) are also produced in plants and are stress-induced. In animals, endo-siRNAs are produced from transposons, heterochromatic sequences, and mRNAs, and are involved in transposon silencing. In flies and mammals, endo-siRNAs are 21 nt long and are produced by Dicer. They are involved in maintaining germ line stability and fertility. In mice, endo-siRNAs are produced from transposons and are involved in DNA methylation. miRNAs are derived from precursor transcripts and are processed by Drosha and Dicer into 21-24 nt duplexes. They regulate gene expression by binding to complementary sites in mRNA 3' UTRs, often repressing translation or inducing cleavage. miRNAs are involved in diverse cellular pathways and are crucial for development and disease. piRNAs are the longest small RNAs and are involved in germ line development, particularly in silencing transposons. piRNAs are produced from long, single-stranded precursor RNAs and are involved in maintaining germ line stability and fertility. Small RNA pathways are interconnected and interact at multiple levels, competing for substrates and effector proteins. They are involved in gene regulation, transposon silencing, and genome protection. The study of small RNAs has revealed their roles in various