  We use maximum entropy arguments to derive the phase space distribution of a
virialized dark matter halo. Our distribution function gives an improved
representation of the end product of violent relaxation. This is achieved by
incorporating physically motivated dynamical constraints (specifically on
orbital actions) which prevent arbitrary redistribution of energy.
  We compare the predictions with three high-resolution dark matter simulations
of widely varying mass. The numerical distribution function is accurately
predicted by our argument, producing an excellent match for the vast majority
of particles.
  The remaining particles constitute the central cusp of the halo (<4% of the
dark matter). They can be accounted for within the presented framework once the
short dynamical timescales of the centre are taken into account.
