Small RNAs are a diverse class of non-coding RNAs, typically 18–30 nucleotides in length, including miRNAs, piRNAs, endogenous siRNAs (endo-siRNAs), and snoRNAs. miRNAs, one of the most widely studied classes, are typically 20–24 nucleotides long and are found in both animals and plants. In animals, miRNAs commonly regulate gene expression by repressing translation and/or promoting target mRNA degradation. In plants, miRNAs frequently direct cleavage of target mRNAs. Sequencing is performed on the Illumina platform, with miRNA analysis available for species with a reference genome.