Diffraction grating rhombs, consisting of two identical gratings, are commonly used as laser beam sampling components exhibiting no angular dispersion. Three conditions must be strictly maintained if two gratings placed in series are to form a grating rhomb: the grating substrates must be parallel, the gratings must be rotated in their own planes so that the grooves are parallel, and they must have equal periods. The detailed behavior of grating rhombs is investigated by cascading the grating equation. The shift-invariant property of diffraction gratings in direction cosine space is utilized to describe "conical" (out-of-plane) diffraction behavior. A detailed grating rhomb alignment sensitivity analysis has been performed and sensitivity curves illustrate the effects of misalignments. An interferometric alignment procedure is also discussed.