Nanoscale coherent light sources are an important part of nano and quantum technologies. Active plasmonic lattices have attracted much interest because they have recently experimentally verified both lasing action and Bose-Einstein condensation (BEC). Tuning the optical and geometric properties of these lattices allows for a crossover between the laser and the BEC phenomenon. This project develops a comprehensive theoretical and computational model for studying these phenomena in plasmonic lattices. We aim to build a model that deals with the interaction of inhomogeneous light fields with the quantum mechanical nature of active molecules, even at the boundary of strong coupling. The model is tested in close co-operation with experiments in the same team. The aim is to produce new fundamental information about the interaction of light and matter in the nanoscale, based on new kinds of coherent nanoscale light sources.