The antireflection coatings which are used on lenses and other optical interfaces can have a profound effect on the image quality formed by an optical system. This paper evaluates the effects on optical performance of s- and p-phase shifts due to coatings. Coating design and lens design are usually treated as separate tasks, since the coating-induced wavefront aberrations are considered insignificant. As demands on optical systems increase (NA>0.9, wavelength <400nm, strehl ratio >95%), it is shown, that coating induced-wavefront aberrations can be the dominating aberration within an optical system. The wavefront aberrations induced by different antireflection coatings on an optical imaging system are numerically evaluated as an example. It is concluded that coating design and optical design have to be optimized in one task to achieve the best optical performance.