Receptors of the LIN-12/Notch family mediate cell-cell interactions during animal development, and aberrations in LIN-12/Notch signaling have been implicated in human disease. Studies in C. elegans have been instrumental in defining the basic features of the LIN-12/Notch pathway, the role of LIN-12/Notch proteins as receptors for intercellular signals, the mechanism of signal transduction, and the regulation of LIN-12/Notch signaling during cell fate decisions. This chapter is focused on detailing how the "awesome power of C. elegans genetics" has identified many core components and modulators of LIN-12/Notch activity.