We use the early C. elegans embryo as a model system to understand how cells form and dynamically stabilize cell polarity. In the one-cell C. elegans zygote, polarity is encoded by asymmetric distributions of conserved polarity determinants known as the PAR proteins. These asymmetries are established in response to a transient sperm-derived cue and then maintained by a complex network of interactions among the PAR proteins, small GTPases, and a dynamic actomyosin cytoskeleton. We combine molecular genetics with powerful new microscopy tools (e.g. single molecule imaging and particle tracking analysis) and mathematical modeling to identify the core design principles that govern this fundamental process.