  We consider dissipative atom-cavity systems and show that their collective
dynamics leads to the maximization of entanglement for intermediate values of
the cavity leakage parameter $\kappa$. We discuss possible ways the reservoir
influences entanglement. We first consider the entanglement of a single
two-level atom with a microwave cavity that is coupled to another cavity. We
show that the atom-cavity entanglement can be made to increase with cavity
leakage. We next show that the entanglement between two atoms passing
successively through a cavity can be maximised for intermediate values of
$\kappa$. We finally consider the micromaser where the increase of two-atom
entanglement for stronger cavity-environment coupling is demonstrated for
experimentally attainable values of the micromaser parameters.
