A review of grazing‐incidence optical design fundamentals is presented with special emphasis on mirror material and surface roughness considerations. Angle‐resolved scattering results on polished and diamond‐turned soft x‐ray mirrors are reviewed, along with the elements of optical scattering theory applied to soft x‐rays. Reflective filtering of higher‐order radiation in monochromator output beams is presented, comparing the transmission and rejection characteristics of one‐, two‐, and three‐reflection filters.