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MicroRNAs (miRNAs) regulate gene expression for diverse functions, but only a limited number of mRNA targets have been experimentally identified. We show that GW182 family proteins AIN-1 and AIN-2 act redundantly to regulate the expression of miRNA targets, but not miRNA biogenesis. Immunoprecipitation (IP) and mass spectrometry indicate that AIN-1 and AIN-2 interact only with miRNA-specific Argonaute proteins ALG-1 and ALG-2 and with components of the core translational initiation complex. Known miRNA targets are enriched in AIN-2 complexes, correlating with the expression of corresponding miRNAs. Combining IP with pyrosequencing and microarray analysis of RNAs associated with AIN-1/AIN-2, we identified 106 previously annotated miRNAs plus nine new candidate miRNAs, but nearly no siRNAs, and more than 3500 potential miRNA targets, including nearly all known ones. Our results …