This article compares and contrasts linear stability analyses based on the deformations of an infinite liquid column and due to boundary-layer vorticity imparted to the free surface from the orifice exit plane. The bulk of the prior works, which date back to Kelvin-Helmholtz [1], Rayleigh [2], Weber [3], Taylor [4], Ponstein [5], Levich [6], Sterling and Sleicher [7], and Reitz and Bracco [8] have focused on the liquid column analysis. Though used to a lesser extent, the boundary-layer instability analysis by Brennen [9] can also be used to predict the dominant wavelength of the laminar jet. Differences between the two approaches are highlighted for sample injection conditions and injector geometries.