This document discusses satellite RNA (satRNA), which are small non-coding RNA molecules that depend on a helper virus for replication and movement in plants. SatRNAs can modulate symptoms caused by their helper virus, either attenuating or exacerbating them. They are classified based on their size, shape, and genome type. SatRNAs encode proteins in some cases that are involved in replication, movement, or suppression of RNA silencing pathways. Their small size makes satRNAs useful for expressing foreign genes in plants and studying virus replication and movement.