  The temperature anisotropies and polarization of the cosmic microwave
background (CMB) radiation provide a window back to the physics of the early
universe. They encode the nature of the initial fluctuations and so can reveal
much about the physical mechanism that led to their generation. In this
contribution we review what we have learnt so far about early-universe physics
from CMB observations, and what we hope to learn with a new generation of
high-sensitivity, polarization-capable instruments.
