The discovery that extracellular signals funnel through receptor-operated pathways to intracellular calcium flux via inositol trisphosphate and diacylglycerol established calcium signaling as a central organizing principle. Calmodulin emerges as a universal calcium sensor coordinating a broad network of kinases, channels, and metabolic regulators, while cyclic adenosine monophosphate–dependent signaling links receptor pathways to energy homeostasis and membrane function. Receptor-level phosphorylation and kinase regulation are recognized as dynamic control points, aligning phosphoinositide signaling with protein kinase cascades across diverse cell types. Methodologically, researchers emphasize biochemical dissection of second messengers, lipid signaling, and early kinase biochemistry, fostering cross-talk and systems-level thinking in signaling networks. Historical Significance: The period marks the birth of the inositol trisphosphate–Ca2+ axis as a canonical signaling mechanism, guiding subsequent pharmacology and cellular biology. Foundational work positions protein kinase C as a Ca2+-activated, diacylglycerol-regulated hub that transduces surface cues into a spectrum of responses and tumor-promoting processes. Calmodulin is established as the master calcium sensor, shaping a universal framework for Ca2+-dependent regulation across enzymes, channels, and transcriptional networks. The era also consolidates receptor-mediated regulation and kinase dynamics, setting the stage for later elaboration of signaling networks and cross-talk among pathways.