Tillering is a crucial trait closely associated with yield potential and environmental adaptation in cereal crops, regulated by the synergy of endogenous (genetic) and exogenous (environmental) factors. The physiological and molecular regulation of tillering has been intensively studied in rice and wheat. However, tillering research on barley is scarce. This review used the recent advances in bioinformatics to map all known and potential barley tiller development genes with their chromosomal genetic and physical positions. Many of them were mapped for the first time. We also discussed tillering regulation at genetic, physiological, and environmental levels. Moreover, we established a novel link between the genetic control of phytohormones and sugars with tillering. We provided evidence of how environmental cues and cropping systems help optimize the tiller number. This comprehensive review enhances the understanding of barley's physiological and genetic mechanisms controlling tillering and other developmental traits.