MACH2: A Two-Dimensional Magnetohydrodynamic Simulation Code for Complex Experimental Configurations. MACH2 is a flexible and powerful two-dimensional magnetohydrodynamic simulation code designed specifically to handle complex experimental configurations. The code’s capabilities include a numerically generated solution-adaptive grid which permits it to be used for either Eulerian or Lagrangian flow problems, use of real equations of state and transport properties from the Los Alamos National Laboratory SESAME package, and a multigrid implicit magnetic field diffusion solver which can be used to simulate problems with vacuum. The descriptive power of the namelist-based problem input language is sufficient that no code modifications are required to set up any of a broad class of problems. Almost no knowledge of the internal data structures and numerical techniques is required to do simulations that realistically model complex experiments. This is made possible by the code’s multiblock architecture and table-driven control structure. Code reliability and flexibility are ensured and enhanced by a structured and modular implementation of boundary conditions and block coupling. This report details the physical model, including boundary conditions; permissible problem geometries; time differencing; and spatial discretization, centering, and differencing of MACH2.