<p>Stay cables with lamp attachments are susceptible to galloping instability; however, this galloping is not well characterized, primarily due to the peculiar inclined-yawed cable attitude. In this study, three-dimensional nonlinear coupled galloping of lamp-attached stay cables is investigated via quasi-steady analysis and unsteady experiments. To this goal, an analysis framework is developed to determine the quasi-steady galloping behavior of inclined cables under yaw winds. In this framework, based on wind velocity decomposition, the complex eigen-solution is formulated using the Galerkin discretization of the equations of motion for cable-wind systems, together with the linearization of self-excited aerodynamic forces. This framework is applied to estimate the galloping characteristics of a stay cable, including critical velocity, post-critical amplitude, and unfavorable wind conditions. Furthermore, wind tunnel experiments on an inclined-yawed cable model are conducted to determine unsteady galloping oscillations. The analytical and experimental results show that the cables exhibit galloping instabilities at multiple yaw angles, even at low wind velocities. The quasi-steady approach provides a relatively reasonable identification of the yaw angles at which galloping occurs and a rough characterization of the nonlinear oscillations, whereas it may somewhat underestimate the critical galloping velocities.</p>