The calcium-sensing receptor (CASR) regulates the NLRP3 inflammasome through intracellular calcium (Ca²⁺) and cyclic AMP (cAMP). Mutations in the NLRP3 gene cause cryopyrin-associated periodic syndromes (CAPS), a group of autoinflammatory diseases. The NLRP3 inflammasome is a key component of cytoplasmic multiprotein complexes that mediate the maturation of the proinflammatory cytokine interleukin-1β (IL-1β) by activating caspase-1. While several models for inflammasome activation have been proposed, the precise molecular mechanism of NLRP3 inflammasome activation and how CAPS-associated mutations activate NLRP3 remain unclear. This study shows that the CASR activates the NLRP3 inflammasome through increased intracellular Ca²⁺ and decreased cAMP. Ca²⁺ or other CASR agonists activate the NLRP3 inflammasome in the absence of exogenous ATP, whereas knockdown of CASR reduces inflammasome activation in response to known NLRP3 activators. CASR activates the NLRP3 inflammasome via phospholipase C, which catalyzes inositol-1,4,5-trisphosphate production and induces Ca²⁺ release from endoplasmic reticulum stores. Increased intracellular Ca²⁺ promotes the assembly of inflammasome components, and intracellular Ca²⁺ is required for spontaneous inflammasome activity in cells from CAPS patients. CASR stimulation also results in reduced intracellular cAMP, which independently activates the NLRP3 inflammasome. cAMP binds to NLRP3 directly to inhibit inflammasome assembly, and downregulation of cAMP relieves this inhibition. The binding affinity of cAMP for CAPS-associated mutant NLRP3 is substantially lower than for wild-type NLRP3, and the uncontrolled mature IL-1β production from CAPS patients' peripheral blood mononuclear cells is attenuated by increasing cAMP. These findings indicate that Ca²⁺ and cAMP are two key molecular regulators of the NLRP3 inflammasome that have critical roles in the molecular pathogenesis of CAPS. The study also shows that extracellular Ca²⁺ activates the NLRP3 inflammasome through CASR, and that the recognition of extracellular Ca²⁺ through CASR activates the NLRP3 inflammasome. The study further demonstrates that CASR is an upstream gatekeeper of the NLRP3 inflammasome. Intracellular Ca²⁺ signaling is important for NLRP3 inflammasome activation induced by extracellular ATP. Elevation of extracellular Ca²⁺ concentrations or other CASR agonists commonly elicits intracellular Ca²⁺The calcium-sensing receptor (CASR) regulates the NLRP3 inflammasome through intracellular calcium (Ca²⁺) and cyclic AMP (cAMP). Mutations in the NLRP3 gene cause cryopyrin-associated periodic syndromes (CAPS), a group of autoinflammatory diseases. The NLRP3 inflammasome is a key component of cytoplasmic multiprotein complexes that mediate the maturation of the proinflammatory cytokine interleukin-1β (IL-1β) by activating caspase-1. While several models for inflammasome activation have been proposed, the precise molecular mechanism of NLRP3 inflammasome activation and how CAPS-associated mutations activate NLRP3 remain unclear. This study shows that the CASR activates the NLRP3 inflammasome through increased intracellular Ca²⁺ and decreased cAMP. Ca²⁺ or other CASR agonists activate the NLRP3 inflammasome in the absence of exogenous ATP, whereas knockdown of CASR reduces inflammasome activation in response to known NLRP3 activators. CASR activates the NLRP3 inflammasome via phospholipase C, which catalyzes inositol-1,4,5-trisphosphate production and induces Ca²⁺ release from endoplasmic reticulum stores. Increased intracellular Ca²⁺ promotes the assembly of inflammasome components, and intracellular Ca²⁺ is required for spontaneous inflammasome activity in cells from CAPS patients. CASR stimulation also results in reduced intracellular cAMP, which independently activates the NLRP3 inflammasome. cAMP binds to NLRP3 directly to inhibit inflammasome assembly, and downregulation of cAMP relieves this inhibition. The binding affinity of cAMP for CAPS-associated mutant NLRP3 is substantially lower than for wild-type NLRP3, and the uncontrolled mature IL-1β production from CAPS patients' peripheral blood mononuclear cells is attenuated by increasing cAMP. These findings indicate that Ca²⁺ and cAMP are two key molecular regulators of the NLRP3 inflammasome that have critical roles in the molecular pathogenesis of CAPS. The study also shows that extracellular Ca²⁺ activates the NLRP3 inflammasome through CASR, and that the recognition of extracellular Ca²⁺ through CASR activates the NLRP3 inflammasome. The study further demonstrates that CASR is an upstream gatekeeper of the NLRP3 inflammasome. Intracellular Ca²⁺ signaling is important for NLRP3 inflammasome activation induced by extracellular ATP. Elevation of extracellular Ca²⁺ concentrations or other CASR agonists commonly elicits intracellular Ca²⁺