Abscisic acid (ABA) is a key plant hormone that regulates various developmental processes and stress responses. Recent research has identified ABA receptors and clarified how key regulatory phosphatase and kinase activities are controlled by ABA. A new model proposes that ABA receptors, such as PYR/PYL/RCAR, function at the apex of a negative regulatory pathway to directly regulate PP2C phosphatases, which in turn regulate SnRK2 kinases. This model unifies many previously defined signaling components and highlights the importance of future work focused on defining the direct targets of SnRK2s and PP2Cs, dissecting the mechanisms of hormone interactions, and defining connections between additional known signaling components and this pathway. ABA was discovered in the 1960s and has since been shown to regulate plant growth and development, including seed development, dormancy, germination, and reproduction. It also plays a critical role in abiotic and biotic stress responses, such as drought, salinity, and pathogen resistance. ABA's physiological effects include regulating water relations, root growth, and the accumulation of osmocompatible solutes and dehydrins to protect cells under stress. ABA's structure is important for its biological activity, with the stereocenter and stereochemistry of the molecule playing a key role. ABA receptors, such as PYR/PYL/RCAR, are involved in ABA signaling and have been shown to bind ABA with high specificity. These receptors are part of a larger family of proteins that may be involved in ABA signaling. Protein phosphatases, such as PP2Cs, are involved in ABA signaling and act as negative regulators of the pathway. They regulate the activity of SnRK2 kinases, which are essential for ABA signaling. PP2Cs are also involved in the regulation of other signaling pathways, including those related to stress responses. Protein kinases, such as SnRK2s, are involved in ABA signaling and play a critical role in regulating gene expression in response to ABA. These kinases are activated by ABA and are involved in the regulation of stomatal closure, seed germination, and other stress responses. ABA-regulated gene expression involves changes in transcription, transcript processing, and stability. ABA induces the expression of genes involved in stress tolerance, such as dehydrins and enzymes that detoxify reactive oxygen species. ABA also represses genes associated with growth, such as those involved in cell wall and chloroplast function. The regulatory elements responsible for ABA-induced changes in gene expression include ABA response elements (ABREs) and other sequences recognized by transcription factors. These elements are involved in the regulation of gene expression in response to ABA and other stresses. The identification of these regulatory elements has been facilitated by biochemical and genetic approaches.Abscisic acid (ABA) is a key plant hormone that regulates various developmental processes and stress responses. Recent research has identified ABA receptors and clarified how key regulatory phosphatase and kinase activities are controlled by ABA. A new model proposes that ABA receptors, such as PYR/PYL/RCAR, function at the apex of a negative regulatory pathway to directly regulate PP2C phosphatases, which in turn regulate SnRK2 kinases. This model unifies many previously defined signaling components and highlights the importance of future work focused on defining the direct targets of SnRK2s and PP2Cs, dissecting the mechanisms of hormone interactions, and defining connections between additional known signaling components and this pathway. ABA was discovered in the 1960s and has since been shown to regulate plant growth and development, including seed development, dormancy, germination, and reproduction. It also plays a critical role in abiotic and biotic stress responses, such as drought, salinity, and pathogen resistance. ABA's physiological effects include regulating water relations, root growth, and the accumulation of osmocompatible solutes and dehydrins to protect cells under stress. ABA's structure is important for its biological activity, with the stereocenter and stereochemistry of the molecule playing a key role. ABA receptors, such as PYR/PYL/RCAR, are involved in ABA signaling and have been shown to bind ABA with high specificity. These receptors are part of a larger family of proteins that may be involved in ABA signaling. Protein phosphatases, such as PP2Cs, are involved in ABA signaling and act as negative regulators of the pathway. They regulate the activity of SnRK2 kinases, which are essential for ABA signaling. PP2Cs are also involved in the regulation of other signaling pathways, including those related to stress responses. Protein kinases, such as SnRK2s, are involved in ABA signaling and play a critical role in regulating gene expression in response to ABA. These kinases are activated by ABA and are involved in the regulation of stomatal closure, seed germination, and other stress responses. ABA-regulated gene expression involves changes in transcription, transcript processing, and stability. ABA induces the expression of genes involved in stress tolerance, such as dehydrins and enzymes that detoxify reactive oxygen species. ABA also represses genes associated with growth, such as those involved in cell wall and chloroplast function. The regulatory elements responsible for ABA-induced changes in gene expression include ABA response elements (ABREs) and other sequences recognized by transcription factors. These elements are involved in the regulation of gene expression in response to ABA and other stresses. The identification of these regulatory elements has been facilitated by biochemical and genetic approaches.