We derive a continuum theory for the phase transition in a classical dimer model on the cubic lattice, observed in recent Monte Carlo simulations. Our derivation relies on the mapping from a three-dimensional classical problem to a two-dimensional quantum problem, by which the dimer model is related to a model of hard-core bosons on the kagomé lattice. The dimer-ordering transition becomes a superfluid-Mott insulator quantum phase transition at fractional filling, described by an SU(2)-invariant continuum theory.PACS numbers: 64.60. Bd, 64.70.Tg, 75.10.Hk The standard model of symmetry-breaking phase transitions, both classical and quantum, is the LandauGinzburg-Wilson (LGW) theory [1], where the critical properties are described by a continuum theory written in terms of the order parameter of the transition. It has recently been argued, however, that in certain twodimensional quantum systems, continuous phase transitions are possible between symmetry-breaking states with apparently unrelated order parameters, in conflict with the LGW paradigm [2,3].Another class of non-LGW transitions occurs in classical systems with constraints that prevent a fully disordered state [4]. As the temperature is raised, these systems instead enter a 'Coulomb phase', where correlation functions have power-law forms and strong directional dependence. A naïve application of the LGW theory fails to capture these correlations and so cannot describe a transition between an ordered phase and a Coulomb phase [5].Recent numerical work [4,6] indicates that such a transition exists in a classical dimer model on the cubic lattice. This model describes the statistics of close-packed 'dimers', objects that occupy two neighbouring sites of the lattice, with every site of the cubic lattice covered by precisely one dimer. There are many configurations that obey this constraint, and if all are given equal weight, the system displays a Coulomb phase [9]. If instead they are given Boltzmann weights that favour parallel dimers, the system orders at low temperatures; the ordered phase is a six-fold degenerate crystal, breaking the lattice symmetry.In this Letter, we outline two steps that lead to a continuum description of this classical dimer transition. Our first step uses the standard mapping between classical statistical mechanics in 3D and quantum mechanics in 2D, and so provides a bridge between the two classes of proposed non-LGW transitions. In the second step, we show that long-wavelength properties at the resulting 2D quantum transition are described by the SU(2)-symmetric noncompact CP 1 (NCCP 1 ) model. This conclusion is consistent with earlier suggestions, on the basis of results for several three-dimensional (3D) quantum models at finite temperature [5,7], that the classical dimer transition should be described by a gauge theory coupled to multiple matter fields.Our approach is to identify the [111] direction as imaginary time and map to a model of hard-core bosons on the kagomé lattice. A related mapping has previously been applied t...