  We have carried out temperature and pressure-dependent Raman and x-ray
measurements on single crystals of Tb$_2$Ti$_2$O$_7$. We attribute the observed
anomalous temperature dependence of phonons to phonon-phonon anharmonic
interactions. The quasiharmonic and anharmonic contributions to the
temperature-dependent changes in phonon frequencies are estimated
quantitatively using mode Gr\"{u}neisen parameters derived from
pressure-dependent Raman experiments and bulk modulus from high pressure x-ray
measurements. Further, our Raman and x-ray data suggest a subtle structural
deformation of the pyrochlore lattice at $\sim$ 9 GPa. We discuss possible
implications of our results on the spin-liquid behaviour of Tb$_2$Ti$_2$O$_7$.
