We introduce a new model describing multiple resonances in Kerr optical cavities. It perfectly agrees quantitatively with the Ikeda map and predicts complex phenomena such as super cavity solitons and coexistence of multiple nonlinear states.Optical resonators featuring Kerr media display a wealth of phenomena, encompassing frequency combs [1], cavity solitons [2,3] and instabilities [4], which are being intensively studied in view of their high impact applications [1]. Given the complexity and the diversity of the physical phenomena, deriving simple, accurate and efficient models is of paramount importance. The workhorse for the description of nonlinear cavity dynamics is the celebrated Lugiato-Lefever equation (LLE) [5,6], which allows for deep theoretical insight and fast and accurate numerical modelling. Despite the fact that the LLE holds valid well beyond the mean-field approximation under which it has been historically derived, it is not capable of modelling all the phenomena of interest. Indeed, LLE can model the evolution of only one Fabry-Pérot mode, that corresponds to a single resonance. Phenomena not captured by LLE range from "super cavity solitons" (SCSs) [7] to the coexistence of stable modulational instability (MI) patterns and solitons, observed in Ref.[8]. The complete and exact dynamical scenario can be reproduced by the famous Ikeda map [9], but this model does not give any reasonable physical insight owing to its complex mathematical structure. A model sharing the accuracy of the Ikeda map and the simplicity of LLE will be of paramount importance in the design of the next-generation of resonators [10]. A reliable model capable to reproduce quantitatively the results of the Ikeda map and the latest experiments [8] is still missing. In this Memorandum, we derive rigorously a multi-resonant LLE system, which agrees quantitatively with the Ikeda map. Each Fabry-Pérot resonance is described by an LLE-type equation, which is coupled to the others in a nontrivial way. An arbitrary number of resonances can be treated, making the model highly flexible and scalable to any situation of experimental interest. For definiteness, we consider a fiber ring cavity, but the method can be of course straightforwardly applied to micro-resonators.We start from the Ikeda map in dimensional units:i ∂EE (n) is the electric field envelope at the n-th round-trip (measured in √ W ), P in = |E in | 2 is the input pump power, ρ 2 , θ 2 are respectively the power reflection and transmission coefficients of the coupler, and φ 0 = β 0 L is the linear cavity round-trip phase shift. For simplicity we lump all the losses in the boundary condition, with 1 − ρ 2 describing the total power lost per roundtrip. Z measures the propagation distance inside the fiber of length L, and T is time in a reference frame traveling at the group velocity of the pulse. To proceed, we note that the map above can be replaced -without loss of generality -with a single equation where the boundary conditions are explicitly incorporated in an NLSEtype...