Inflation, an era of accelerated expansion of the universe prior to the radiation phase, constitutes the paradigm of primordial cosmology. Within this paradigm, the simplest single-field slow-roll models economically explain all curent data. However, the sensitivity of inflation to Planck scale physics, and the fact that ultraviolet completions of inflation invariably involve extra fields coupled to the inflaton, indicate that these models constitute at best a phenomenological description that emerges from a more realistic physical framework.