Quasi-two-dimensional flow describes a condition in which the velocity field may have three non-zero components, but it only depends on two spatial dimensions. The velocity is consequently the same in any cross-sectional plane of the third dimension. The cross-sectional velocity field in a quasi-two-dimensional vortex flow is the same as for a simple two-dimensional vortex flow, but these flows can also exhibit an axial velocity in the vortex core or other flow field orthogonal to the cross-sectional plane. The chapter develops the governing equations for vorticity field in a quasi-two-dimensional flow and then examines several applications of this simplification to vortex flows. Examples include the Batchelor q-vortex, the problem of vorticity expulsion in the presence of an axial shear flow, fluid flow past a yawed cylinder, and a simplified model of turbulent vortex-wall interaction.