A rational method to control morphology of polymer-nanofibers produced by electro- spinning is developed using dimensional analysis of the electrospinning process. The analysis is validated against data sets from the literature, which provides an empirical correlation between fiber size, controllable operating conditions, and measurable spinning solution properties. A stable jet operating regime is identified for which scaling of dimensionless groups is presented. Deviations from this scaling are qualitatively consistent with capillary instability of the electrospinning jet, for which a beaded fiber morphology is obtained. The results provide criteria for designing and controlling electrospinning of polymer solutions and resulting nanofiber morphology. 2006 American Institute of Chemical Engineers AlChE J, 53: 51-55, 2007.