Ca[2+] release-activated Ca[2+] (CRAC) channels function in store-operated Ca[2+] entry, a mechanism for Ca[2+] entry across the plasma membrane (PM) into the endoplasmic reticulum (ER)) Ca[2+] stores. CRAC channels are highly Ca[2+] selective and are composed of Orai pore-forming subunits and the stromal interaction molecule (Stim), a Ca[2+] sensor. When ER Ca[2+] stores are depleted, a conformational change in ER-membrane localized Stim brings it into contact with PM-localized Orai to form a complex, allowing the movement of Ca[2+] from the extracellular milieu directly into the ER lumen. (Adapted from FBrf0251360, FBrf0214207 and PMID:27130253.)