The atomic and electronic structure of both neutral and negatively charged ZrGen (n=1-21) clusters have been studied using ab initio calculations. The atomic structures have been identified by comparing the calculated results of the electronic spectra of the anion clusters with the available photoelectron spectroscopy data. We find that the atomic structure of ZrGen cluster can be derived by adding one or more Ge atoms on smaller clusters. Our results show that in some cases a higher energy isomer of ZrGen anion cluster may be present in experiments, but the neutral of such an anion is often the lowest energy isomer. This shows the importance of the lowest energy isomer of neutral clusters in experiment. In some cases, it is found that two different isomers of the anion of a cluster converge to the identical isomer of the neutral. A large value of the highest occupied molecular orbital-lowest unoccupied molecular orbital gap as well as binding energy per atom has been calculated for ZrGe16 neutral cluster and hence, it is more stable and less reactive as compared to other clusters. This agrees with the high abundance of ZrGe16 cluster in experiments. The Zr atom is encapsulated in a cage-like structure at a size of thirteen or more Ge atoms. This also agrees with the experiments. Further, we have calculated vertical and adiabatic detachment energies and obtained a low value for ZrGe16 also in agreement with experiments. The addition of an electron to a neutral ZrGe11 cluster, however, changes its atomic structure drastically and thus, the calculated adiabatic and vertical detachment energies for ZrGe11 anion differ very significantly. © 2015 Elsevier B.V.