Following experimental realizations of room temperature polariton lasing with organic molecules, we present a microscopic model that allows us to explore the crossover from weak to strong matterlight coupling. We consider a non-equilibrium Dicke-Holstein model, including both strong coupling to vibrational modes and strong matter-light coupling, providing the phase diagram of this model in the thermodynamic limit. We discuss the mechanism of polariton lasing, uncovering a process of self-tuning, and identify the relation and distinction between regular dye lasers and organic polariton lasers.Bose-Einstein statistics underpin both the thermal equilibrium phenomenon of Bose-Einstein condensation, and the non-equilibrium phenomenon of lasing. Lying between these two extremes, there now exist several experimental platforms; in particular exciton-polaritons (quasiparticles resulting from strong coupling between photons and excitons) in semiconductor microcavities at cryogenic temperatures [1][2][3], and photons in dye-filled microcavities at room temperature [4]. Since these microcavities are imperfect, they are sources of coherent light (as is a laser), but differ in mechanism from photon lasing [5,6]. Indeed, polariton lasing does not need electronic inversion, and so it is often stated that it can provide coherent light sources with ultra-low thresholds. Polariton lasing can also occur at room temperature in appropriate materials: inorganic materials such as wide bandgap semiconductors [7-9] and two-dimensional materials [10], and the focus of this Letter, organic materials [11][12][13].Polariton condensation in organic materials prompts interesting questions regarding the mechanisms of polariton relaxation and lasing. Excitons in organic materials are Frenkel excitons -electronic excitations of a molecule or chromaphore delocalized by hopping [14]. Excitons in organic materials typically show complex absorption and emission spectra, due to strong coupling between the electronic state and the nuclear configuration, leading to rovibrational dressing. This causes a Stokes shift, so that emission is at longer wavelengths than absorption. Spectral separation of emission and absorption underpins the operation of dye lasers [15], allowing gain without electronic inversion. Since both strong matterlight coupling and large Stokes shifts are expected to reduce the lasing threshold, how they act in concert is of both fundamental interest and practical relevance.Theoretical modeling of polariton condensates can follow a number of approaches. To describe the macroscopic pattern formation and superfluid hydrodynamics it mostly suffices to use the phenomenological complex Gross-Pitaevskii equation [6,16]. However, such order parameter equations are ubiquitous in non-equilibrium systems breaking U (1) symmetry, so similar equations also apply for a photon laser [17,18]. Such approaches are thus not well suited to understanding the relation between polariton and photon lasing, or the particular properties of organic polaritons. To...