Analysis of the combustion of fuel droplet arrays is constrained by the paucity of information on the effects of droplet interaction on ignition and flame development. An experimental and theoretical examination of the effects of interaction on ignition of a single stream of monosized fuel droplets is described. Experimentally, ignition times were measured for continuous droplet streams injected into a hot gas environment with droplet spacing ranging from hundreds of droplet diameters to slightly less than two diameters, approaching as closely as possible a cylindrical filament of liquid fuel. Apart from the change in symmetry of the environment of any one droplet as droplet spacing is decreased, closer spacing enhances the significance of the diffusion of heat and mass from the flame region surrounding burning droplets to the neighborhood of an unignited droplet. Theoretical models of ignition for the limiting droplet spacings represented by an isolated spherical droplet and a cylindrical filament of liquid are used to provide an understanding of the extent of potential droplet interaction effects on ignition time. The present investigations indicate that as droplet spacing is made smaller, interaction effects become increasingly more important for small droplets, low gas phase temperatures, and fuels of low volatility. Increases in ignition delay times of nearly four-fold are shown to be possible as droplet spacing is made very small, approaching the limit of a cylindrical filament.