Electrical activity participates in the development of the nervous system and comes in two general forms. Use-dependent or experience-driven activity occurs relatively late in development, and is important in events of terminal nervous system differentiation, such as stabilization of synaptic connections. Earlier in development, activity is spontaneous, occurring independently of normal sensory input and motor output. Spontaneous activity participates in many of the initial events of axon outgrowth, pruning of synaptic connections, and maturation of neuronal signaling properties. Despite its importance, the genesis of spontaneous activity is poorly understood. What is clear is that spontaneous activity must be regulated by the patterns with which voltage- and ligand-gated ion channels develop in individual neurons. This review explores how that regulation most likely occurs.