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Calcium (Ca2+) signaling is a fundamental regulator of virtually all aspects of eukaryotic cell physiology, including gene expression, secretion, metabolism, motility, and cell fate decisions. The spatial and temporal control of cytosolic Ca2+ signals relies on a coordinated interplay between intracellular Ca2+ stores and plasma membrane (PM) Ca2+ channels. A critical advance in this field over the past two decades was the molecular identification of stromal interaction molecule 1 (STIM1) as the long-sought Ca2+ sensor that couples depletion of endoplasmic reticulum Ca2+ stores to Ca2+ influx across the PM. STIM1 has been established as a core component of store-operated Ca2+ entry, acting through direct activation of ORAI Ca2+ channels. However, accumulating evidence now indicates that STIM1 functions extend beyond this canonical role. STIM1 participates in the regulation of multiple classes of ion channels, contributes to the organization of membrane contact sites, and acts as a signaling scaffold influencing cellular processes independently of classical store depletion. This review summarizes the discovery and canonical functions of STIM1 and focuses on its emerging non-canonical roles, highlighting how STIM1 has evolved from an ER Ca2+ sensor into a multifunctional signaling hub.