Multiple microRNA (miRNA) variant (isomiR) sequences have been identified at miRNA loci, suggesting that the miRNA sequence is not a single sequence but a series of isomiR sequences with sequence and expression heterogeneities. These isomiRs may be considered a large gene family with diverse expression patterns or a mini-gene cluster with high levels of sequence similarity. Although the isomiRs are diverse and have potentially coordinated relationships in regulatory networks via isomiR-isomiR interactions, they are largely unstudied. External interactions with other RNAs also enrich the cross-talk across different RNA molecules. In the present study, we describe miRNAs/isomiRs and their interactions, and methods and platforms. Interactions with small RNAs may be an internal regulatory pattern and an effective means of achieving synergistic regulation, which provides a new angle to explore the small RNA world.