Target-directed miRNA degradation (TDMD) is a novel mechanism by which miRNAs are selectively degraded through interactions with trigger RNAs. Trigger RNAs, which have high complementarity to miRNAs, recruit the ZSWIM8 E3 ubiquitin ligase, leading to AGO ubiquitination and proteolysis, and subsequent miRNA destruction. TDMD is regulated by ZSWIM8 in bilateral animals, with over 100 miRNAs and hundreds of predicted trigger RNAs. Disruption of individual trigger RNAs or ZSWIM8 has revealed important developmental and physiological roles in various organisms. TDMD involves a conformational change in the AGO–miRNA complex recognized by ZSWIM8, leading to ubiquitination and proteasomal degradation of AGO, and subsequent miRNA degradation. The ZSWIM8 protein has three paralogs, but its functions and substrates are poorly understood. ZSWIM8 is conserved across Bilateria and plays important developmental roles in C. elegans, D. melanogaster, and mice. ZSWIM8 regulates over 100 miRNAs, including 12 in human cells. ZSWIM8 deficiency causes perinatal lethality in mice, likely due to defects in lung sacculation. ZSWIM8 also regulates the axon guidance receptor ROBO3/SAX-3 and neuronal signaling protein Dab1. ZSWIM8 deficiency in Drosophila causes embryonic lethality and affects actin cytoskeleton. ZSWIM8 deficiency in mice causes perinatal and postnatal lethality and abnormal hippocampal patterning and behavioral deficits. ZSWIM8 regulates the Reelin-Dab1 pathway during neurogenesis. ZSWIM8 is involved in miRNA degradation through interactions with AGO proteins and other factors. The structure of ZSWIM8 includes a BC box, Cullin box, and SWIM domain. ZSWIM8 interacts with the E3 ubiquitin ligase complex and is essential for TDMD. ZSWIM8 has been shown to regulate the degradation of miR-7 and miR-27a. ZSWIM8 is involved in viral-host interactions, including the degradation of miR-27a by HSUR1 and miR-27a by m169. ZSWIM8 also regulates cellular homeostasis and regulatory circuits, including cell cycle control and apoptosis. ZSWIM8 is involved in animal development, behavior, and stress response, including the regulation of miR-999 in Drosophila. ZSWIM8 is involved in the degradation of miR-29b in cerebellar granule neurons. ZSWIM8 is involved in the identification and validation of miRNA-trigger RNA pairs through computational predictions and experimental approaches such as AGO-CLASH. Best practices for validatingTarget-directed miRNA degradation (TDMD) is a novel mechanism by which miRNAs are selectively degraded through interactions with trigger RNAs. Trigger RNAs, which have high complementarity to miRNAs, recruit the ZSWIM8 E3 ubiquitin ligase, leading to AGO ubiquitination and proteolysis, and subsequent miRNA destruction. TDMD is regulated by ZSWIM8 in bilateral animals, with over 100 miRNAs and hundreds of predicted trigger RNAs. Disruption of individual trigger RNAs or ZSWIM8 has revealed important developmental and physiological roles in various organisms. TDMD involves a conformational change in the AGO–miRNA complex recognized by ZSWIM8, leading to ubiquitination and proteasomal degradation of AGO, and subsequent miRNA degradation. The ZSWIM8 protein has three paralogs, but its functions and substrates are poorly understood. ZSWIM8 is conserved across Bilateria and plays important developmental roles in C. elegans, D. melanogaster, and mice. ZSWIM8 regulates over 100 miRNAs, including 12 in human cells. ZSWIM8 deficiency causes perinatal lethality in mice, likely due to defects in lung sacculation. ZSWIM8 also regulates the axon guidance receptor ROBO3/SAX-3 and neuronal signaling protein Dab1. ZSWIM8 deficiency in Drosophila causes embryonic lethality and affects actin cytoskeleton. ZSWIM8 deficiency in mice causes perinatal and postnatal lethality and abnormal hippocampal patterning and behavioral deficits. ZSWIM8 regulates the Reelin-Dab1 pathway during neurogenesis. ZSWIM8 is involved in miRNA degradation through interactions with AGO proteins and other factors. The structure of ZSWIM8 includes a BC box, Cullin box, and SWIM domain. ZSWIM8 interacts with the E3 ubiquitin ligase complex and is essential for TDMD. ZSWIM8 has been shown to regulate the degradation of miR-7 and miR-27a. ZSWIM8 is involved in viral-host interactions, including the degradation of miR-27a by HSUR1 and miR-27a by m169. ZSWIM8 also regulates cellular homeostasis and regulatory circuits, including cell cycle control and apoptosis. ZSWIM8 is involved in animal development, behavior, and stress response, including the regulation of miR-999 in Drosophila. ZSWIM8 is involved in the degradation of miR-29b in cerebellar granule neurons. ZSWIM8 is involved in the identification and validation of miRNA-trigger RNA pairs through computational predictions and experimental approaches such as AGO-CLASH. Best practices for validating