Plants can sense the direction of gravity and orient their growth to ensure that roots are anchored in soil and that shoots grow upward. Gravitropism has been studied extensively using Arabidopsis genetics, but the exact mechanisms for gravitropism are not fully understood. Here, we demonstrate that five NPY genes play a key role in Arabidopsis root gravitropism. NPY genes were previously identified as regulators of auxin-mediated organogenesis in way with the AGC kinases PID, PID2, WAG1, and WAG2. We show that all five NPY genes are highly expressdd in primary root tips. The single npy mutants do not display obvious gravitropism defects, but the npyl npy2 npy3 npy5 quinntuple mutants show dramatic gravitropic phenotypes. Systematic analysis of all the npy double, triple, and qudruple combinations demonstrates that the five NPY genes all contribute to gravitropism. Our work indicates that gravitropism,phototropism, and organogenesis use analogous mechanisms in which at least one AGC kinase, one NPH3/NPY gene, and one ARF are required.