Using five independent analytic and Monte Carlo simulation codes, we have studied the performance of wide‐field ground‐layer adaptive optics (GLAO), which can use a single, relatively low order deformable mirror to correct the wave‐front errors from the lowest altitude turbulence. GLAO concentrates more light from a point source in a smaller area on the science detector, but unlike with traditional adaptive optics, images do not become diffraction‐limited. Rather, the GLAO point‐spread function (PSF) has the same functional form as a seeing‐limited PSF and can be characterized by familiar performance metrics such as full width at half‐maximum (FWHM). The FWHM of a GLAO PSF is reduced by 0 farcs1 or more for optical and near‐infrared wavelengths over different atmospheric conditions. For the Cerro Pachón atmospheric model, this correction is even greater when the image quality is poorest, which effectively eliminates "bad seeing" nights; the best seeing‐limited image quality, available only 20% of the time, can be achieved 60%–80% of the time with GLAO. This concentration of energy in the PSF will reduce required exposure times and improve the efficiency of an observatory up to 30%–40%. These performance gains are relatively insensitive to a number of trade‐offs, including the exact field of view of a wide‐field GLAO system, the conjugate altitude and actuator density of the deformable mirror, and the number and configuration of the guide stars.