Summary: Wing rock is a complex phenomenon that occurs as a result of the system’s inherent aerodynamic nonlinearities and is dominant only in the roll motion. It has been intensively investigated on heavily swept delta wings, but limited work has been done on rectangular wings, which are becoming increasingly popular in micro aerial vehicles. This research investigates the wing rock features of a rectangular wing using experimental, numerical, and analytical approaches. Initially, free-to-roll wind tunnel tests using an air bearing-based apparatus are performed. Then, a validated numerical method based on solving the three-dimensional incompressible Reynolds-averaged Navier-Stokes equations is utilized in three different approaches: the static tests, the unsteady forced roll tests, and the unsteady free-to-roll tests. Both unsteady approaches are compared, and the flow-field analysis is done with Liutex, a novel vortex identification method. Afterward, using numerical simulation data, an analytical method based on multiple time scales is modeled and the stability properties are determined using bifurcation analysis. The experimental and numerical results are in good agreement. The findings show that the separation bubble’s movement and interaction with the wingtip vortices are crucial in inducing the wing rock phenomenon in rectangular wings.