Calculations are presented for the influence of isolated magnetic impurities or defects on the spin‐wave spectrum of semi‐infinite ferromagnets and antiferromagnets. A Green’s‐function theory and a Heisenberg model are used to study the spin‐wave excitations associated with a defect at or near a magnetic surface, showing that there may be localized ‘‘defect modes’’ at energies outside the regions of bulk spin waves and surface spin waves. Applications are made to impurities in simple cubic ferromagnets and rutile‐structure antiferromagnets.