Plant growth regulators (PGRs) classically comprise phytohormones, but in recent years, various inhibitors of phytohormone synthesis or translocation and blockers of their receptors have emerged as additional, equally important, growth regulators. While the application of PGRs is becoming increasingly apparent in agriculture, viticulture, and horticulture, ongoing research is focussing on uncovering the complex signalling networks and regulatory processes underlying their actions in a range of plant species. This special issue highlights the latest research in this exciting field, including steps towards enhancing crop yield and resistance to biotic and abiotic stresses (see editorial by Tripathi et al., on pp. 1757-1760).