Learning and memory refer to an animal's ability to respond adequately to environmental signals that may be negative (aversive learning) or positive (appetitive learning) in nature. The extremely elaborate connectivity network of neurons in the brain is capable of governing animals' reactions (e.g., by enhancing or weakening single or multiple synapses). Such circuit plasticity is largely believed to be the very essence of memory formation. It has been suggested that long-term memory, in contrast to short-term memory, requires de novo protein synthesis and can be prevented by protein synthesis inhibitors. The local protein translation in dendrites allows neurons to selectively rebuild only those synapses that have been activated. However, substrates of protein synthesis (i.e., mRNA) have to be kept suppressed until they are needed. MicroRNAs--short, non-protein-coding RNA regulatory sequences that guide an RNA--induced silencing complex to target mRNAs-seem to be perfect candidates in fulfilling this function in neurons. In this article, the authors discuss the recently recognized role of microRNAs as regulators of memory formation and endurance.