MicroRNAs, the class of small ribo-regulators, have been implicated in the regulation of a range of different biological processes, including development and differentiation, proliferation, and cell death. Only for a small fraction of identified microRNAs has a function been elucidated; therefore, a great deal of research remains to be performed to fully understand the role and implications of microRNAs. This chapter discusses protocols for the isolation of microRNAs, reverse transcription, PCR, and large scale profiling using TaqMan low density miRNA arrays for analysis of microRNA expression levels.