  This is a review of the Cold Dark Matter model of structure formation, and
its variants. The approach is largely from first principles, the main aim being
to impart a basic understanding of the relevant theory with an eye to the
likely intense activity of the next few years, but the current observational
status of the model is also critically assessed. The evolution of adiabatic and
isocurvature density perturbations is described, and their effect on the large
scale cmb anisotropy calculated as well as that of any gravitational waves. The
generation of all three types of perturbation during inflation is described,
and the normalisation and spectral indices are calculated in terms of the
inflationary potential and its first and second derivatives. The comparison of
the theory with each type of observation is described, starting with the COBE
data and moving down in scale to the non-linear regime. Constraints on the
spectrum of the adiabatic density perturbation are exhibited, the spectrum
being parametrised by its normalisation and its degree of tilt. Finally
extensions of the CDM model are considered, which replace some of the cold dark
matter by hot dark matter or a cosmological constant.
