This paper investigate;< the influence of in-plane restraints on the buckling behaviour of plates under uniform compression, shear and in-plane bending. Most of the design expressions and the numerical data available in the literature are based on the assumption that the plate is free to move laterally and, hence, the restraints imposed by the attached elements against this motion are ignored. In this paper the induced stresses due to lateral restraints are derived and the mathematical formulation for analyzing the plate with longitudinal edges partially restrained against rotation is presented. Results are then presented showing the variation of K and the associated buckling mode for the full range of lateral restraint, LY, from edges free to move, (Y = 0, to fully restrained edges, (Y = 1, for various plate aspect ratios and stress gradient coefficients. Also, a comparison is made between the buckling loads predicted from various formulas in stability standards, based on free edge translation, .uid the values derived from the present investigation. A difference of about 35% in the predicted buckling load will be found which shows the importance of defining the in-plane boundary condition in the buckling analysis of plates under this type of loading. Moreover, it will be shown that the buckling mode, which is an important quantity in estimating the post-buckling reserve, is also different by 'changing this in-plane boundary condition.