  We discuss the influence of gravitational waves (GWs) upon the polarisation
of the Cosmic Microwave Background Radiation (CMBR). We show how to compute the
{\em rms} temperature anisotropy and polarisation of the CMBR induced by GWs of
arbitrary wavelength. We find that the ratio of polarisation, $\Pi$, to
anisotropy, $A$, can be as large as $\sim 40$\%, but is sensitively dependent
upon the GW spectrum and the cosmological ionisation history. We argue that
CMBR polarisation measurements can provide useful constraints on cosmological
models.
