In order to explore and delimit the full range of phenomenological possibilities inherent within the Dynamical Dark Matter framework, it is necessary to understand how ensembles of unstable particles are constrained by data.  In this connection, cosmological constraints on the decays of such particles play a particularly important role.  Indeed, such decays can lead to a variety of observable effects which are tightly constrained by data --- effects which include the alteration of the primordial abundances of light nuclei, distortions in the CMB-photon spectrum, the modification of the ionization history of the universe, and additional contributions to the diffuse extra-galactic photon flux.  While the bounds that these considerations impose on a single decaying particle species are well established, the corresponding bounds on ensembles of decaying particles are less well understood.  Motivated by these considerations, in this talk, I examine the cosmological constraints on ensembles of decaying particles.  Moreover, I show that each of these constraints can be approximated by a set of simple analytic expressions which can be applied generically to almost any ensemble of late-decaying particles.  Indeed, these results transcend the Dynamical Dark Matter framework and have broader implications for other ensembles of unstable particles as well.