We develop three main topics in support of further understanding and specifying wavefront aberrations from the lithographer's point of view. The concept of the Magnitude Weighted Aberration is introduced providing a convenient and rapid numerical method for assessing the interaction of wavefront aberrations with reticle pattern and illumination mode. This analysis suggests that the advanced lithographic lens user will require unprecedented correction on the total wavefront aberration to realize the full potential of the imaging system in high yielding integrated circuit fabrication. Specific details on the required aberration control are provided with a Monte Carlo tolerancing analysis of the RMS wavefront error using lithographic CD control and pattern placement as quality metrics. Patten placement proves to be as sensitive to wavefront aberrations as CD control forcing a tight specification on the asymmetric aberration components even when a large focus and exposure latitude is available. Based on the wavefront specifications generated it is imperative that the lithographic lens user be able to independently de-couple and quantify the state of certain aberration coefficients. Toward this goal, we demonstrate an aberration reverse engineering procedure using experimental pattern placement error as the input response.