The seaside sparrow (Ammospiza maritima) is an American sparrow.
Adults have brownish upperparts with gray on the crown and nape, and a grayish-buff-colored breast with dark streaks; they have a dark face with gray cheeks, a white throat, and a short, pointed tail. Birds show a small yellow streak just above the eye.
Their breeding habitat is salt marshes on the Atlantic and Gulf coasts of the United States from southern New Hampshire to southern Texas. The nest is an open cup usually built in the salt marsh on tidal reeds and spartina grasses.