Abscisic acid-insensitive 5 (ABI5), a plant basic leucine zipper (bZIP) transcription factor, has been revealed to be the key regulator in the abscisic acid (ABA) signaling pathway controlling seed dormancy, germination, plant growth, and flowering time. Recently, new evidence has come to light that a combination of different post-translational modifications (PTMs) might together control the stability and activity of ABI5. In this review, we highlight three types of PTM (protein phosphorylation/dephosphorylation, ubiquitination, and sumoylation) and their interactions that precisely regulate ABI5 signaling. ABI5 is the best-studied key molecule in the ABA signaling pathway with respect to PTMs; therefore, this review could serve as a model to guide post-translational studies of important regulators in other plant hormone signaling pathways.