A four-step mechanism is hypothesized for the process of fiber formation by interfacial polyelectrolyte complexation: (1) formation of a polyionic complex film at the interface that acts as a viscous barrier to free mixing; (2) scattering of this complex by a drawing motion, creating submicron "nuclear fibers"; (3) growth of "nuclear fibers", with an accompanying decrease in the viscosity of the surrounding polyelectrolyte matrix; (4) coalescence of "nuclear fibers", resulting in a thicker primary fiber and gel droplets at regular intervals along its axis. Presented evidence include light and confocal microscopy of the fiber structure, detailed observation of the fiber drawing process, turbidity experiments to measure the stability of the interface, effect of polyelectrolyte solution concentrations and contact area at the interface on fiber dimensions, and identification of two critical draw rates that can be related to the proposed fiber-forming mechanism.