MicroRNAs are endogenous small RNAs known to be key regulators of gene expression in animals and plants. They are defined by their specific biogenesis which involves the precise excision from an imperfect fold-back precursor. These precursors contain structural determinants required for their correct processing. Still, there are significant differences in the biogenesis and activities of plant and animal microRNAs. This review summarizes diverse aspects of precursor processing in plants, contrasting them to their animal counterparts.