Abstract: Abscisic acid (ABA) is an important plant phytohormone and plays a key role in the regulation of seed development, dormancy, and germination, plant growth and flowering inhibition, and abiotic stress response pathways. ABA also interacts with other plant hormones, such as auxin and ethylene, to precisely regulate root growth, including that of preprimary roots, lateral roots, and root hairs. In this updated review, we summarize the molecular mechanisms by which ABA regulates plant root growth and development, focusing on the model plant Arabidopsis thaliana (L.) Heynh. We also discuss the proposed mechanism of ABA interaction with other plant hormones (such as GA) to regulate root growth, especially under abiotic stress conditions. Additionally, the future research directions in this field are discussed.