  The inclusion of physical effects from sea quarks has been one of the main
advances in lattice QCD simulations over the last few years. We report on
recent studies with four flavours of dynamical quarks and address some of the
potential issues arising in this new setup. First results for physical
observables in the light, strange and charm sectors are presented together with
the status of dedicated simulations to perform the non-perturbative
renormalisation in mass-independent schemes.
