With lithography parameters approaching their limits, continuous improvement requires increasing dialogues and compromises between the technology and design communities. Only with such communication can semiconductor manufacturers reach the 30 nm physical-gate-length era with optical lithography. Optical lithography is an enabling technology for transistor miniaturization. With the wavelength and numerical aperture of exposure systems approaching their limits, the semiconductor industry needs continuous reduction of the k₁ factor. Challenges include image quality improvement, proximity effect correction, and cost control. An indispensable ingredient for future success is improvement in the design-manufacture interface.