Abstract: A device manufacturing method is disclosed in which the aberration of the projection system of a lithographic projection apparatus is obtained in terms of the Zernike expansion. The field distribution of displacement error and focal plane distortion of the projected image are calculated on the basis of the Zernike aberration and sensitivity coefficients which quantify the relationship between Zernike aberration components and the error in the image. A calculation is then performed to determine the compensation to apply to the apparatus in order to minimize the error in the image. The compensation is then applied to the apparatus. The compensation may comprise increasing one component of aberration of the apparatus in order to decrease the effect of another aberration, such that, on balance, the image quality as a whole is improved.