  The observational constraints on the primordial power spectrum have tightened
considerably with the release of the first year analysis of the WMAP
observations, especially when combined with the results from other CMB
experiments and galaxy redshift surveys. These observations allow us to
constrain the physics of cosmological inflation: (i) The data show that the
Hubble distance is almost constant during inflation. While observable modes
cross the Hubble scale, it changes by less than 3% during one e-folding:
d(d_H)/dt < 0.032 at 2 sigma. The distance scale of inflation itself remains
poorly constrained: 1.2 x 10^{-28} cm < d_H < 1 cm. (ii) We present a new
classification of single-field inflationary scenarios (including scenarios
beyond slow-roll inflation), based on physical criteria, namely the behaviour
of the kinetic and total energy densities of the inflaton field. The current
data show no preference for any of the scenarios. (iii) For the first time the
slow-roll assumption could be dropped from the data analysis and replaced by
the more general assumption that the Hubble scale is (almost) constant during
the observable part of inflation. We present simple analytic expressions for
the scalar and tensor power spectra for this very general class of inflation
models and test their accuracy.
