Circulators which can be operated at cryogenic temperatures are discussed. Both symmetrical Y‐junction circulators using polycrystalline ferrimagnetic garnets and hybrid‐gyrator circulators using single crystals are evaluated. The temperature dependence of the ferromagnetic resonance losses of polycrystalline aluminum‐doped and undoped yttrium iron garnet is reported. Device performance is evaluated in terms of the measured material properties.