The flow development and instability characteristics of rectangular liquid jets were experimentally and theoretically investigated. Rayleigh's classical analysis for estimating axis-switching wavelength was revisited and two separate functions representing aspect ratio and shape type were identified. The predictive accuracy of Rayleigh's model, the difference between the predicted values and the actual measured values, was shown to be about 20%. The function representing the influence of aspect ratio was modified, our modified function brought the predictive accuracy to about 2%. Six rectangular nozzles of equivalent cross sectional area with aspect ratios of 1, 2, 3, 4, 5 and 6 were manufactured. The tests were performed for the mass flow rates varying from 0.8 to 44.4g/s. High speed photography and shadowgraphy technique were employed to capture the instantaneous flow dynamics of the liquid jets. A non-linear regression analysis was used to express the dependency of the axis-switching wavelength on the jet aspect ratio and flow Weber number. The predictive accuracy of the regression model was about 7%, less than our modified theory, indicating that our modified model had captured more of the flow physics hence was better able to predict the flow features than the simple regression analysis of experimental data. Based on our experimental data a single linear correlation was developed for the breakup length of rectangular jets of all aspect ratios in the second wind-induced regime. (C) 2019 Elsevier Ltd. All rights reserved.