We introduce a numerical framework, the Voronoi Implicit Interface Method for tracking multiple interacting and evolving regions (phases) whose motion is determined by complex physics (fluids, mechanics, elasticity, etc.), intricate jump conditions, internal constraints, and boundary conditions. The method works in two and three dimensions, handles tens of thousands of interfaces and separate phases, and easily and automatically handles multiple junctions, triple points, and quadruple points in two dimensions, as well as triple lines, etc., in higher dimensions. Topological changes occur naturally, with no surgery required. The method is first-order accurate at junction points/lines, and of arbitrarily high-order accuracy away from such degeneracies. The method uses a single function to describe all phases simultaneously, represented on a fixed Eulerian mesh. We test the method's accuracy through convergence tests, and demonstrate its applications to geometric flows, accurate prediction of von Neumann's law for multiphase curvature flow, and robustness under complex fluid flow with surface tension and large shearing forces.multiple interface dynamics | level set methods | foams | minimal surfaces T here are a host of physical problems that involve interconnected moving interfaces, including dry foams, crystal grain growth, mixing of multiple materials, and multicellular structures. These interfaces are the boundaries of individual regions/cells, which we refer to as phases. The physics, chemistry, and mechanics that drive the motion of these interfaces are often complex, and include topological challenges when interfaces are destroyed and created.Producing good mathematical models that capture the motion of these interfaces, especially at degeneracies, such as triple points and triple lines where multiple interfaces meet, is challenging. Building robust numerical methods to tackle these problems is equally difficult, requiring numerical resolution of sharp corners and singularities, and recharacterization of domains when topologies change. A variety of methods have been proposed to handle these problems, including (i) front tracking methods, which explicitly track the interface, modeled as moving segments in two dimensions and moving triangles in three dimensions, (ii) volume of fluid methods, which use fixed Eulerian cells and assign a volume fraction for each phase within a cell, (iii) level set methods (1), which use an implicit formulation to represent the interface, and treat each region/phase separately, followed by a repair procedure which reattaches the evolving regions to each other (1-3), and (iv) diffusion generated motion which combine diffusion via convolution with reconstruction procedures to simulate multiphase mean curvature flow (4). Although there are advantages and disadvantages to each of these approaches, it has remained a challenge to robustly and accurately handle the wide range of possible motions of evolving, highly complex interconnected interfaces separating a large number of phases un...