Eukaryotic cells express small noncoding RNAs to silence target genes or regulate chromatin domains. MicroRNAs (miRNA) are endogenous small RNAs that are thought to each regulate multiple mRNA targets. To gain a deeper understanding of processes regulated by small noncoding RNAs, techniques are required to identify and detect them. This unit describes standard laboratory methods for and comments about high-throughput technologies for the identification and detection of small RNAs. This unit also outlines a cell-based reporter gene assay for assessing the regulatory potential of a microRNA on a candidate mRNA target. (c) 2008 by John Wiley & Sons, Inc.