Age-related hearing loss is a worldwide epidemic characterized by the progressive loss of hair cells, particularly outer hair cells (OHCs). Despite the importance of hair cells, the mechanisms underlying the specification of progenitor cells to functional inner versus outer hair cells are poorly understood. In a highly collaborative study using a combination of methods that range from genetic analysis, single cell RNA-seq, in vivo gene delivery, imaging, and electrophysiology, we recently identified IKZF2 as a critical regulator of the terminal maturation of the outer hair cells (published in Nature, 2018). Importantly, we discovered that viral gene transfer of Ikzf2 to inner HCs (IHCs) can induce a partial molecular and functional conversion of IHCs to OHCs. We continue to study IKZF2 to illuminate outer hair cell development and function.