Amanzi provides a flexible and extensible multiphase, multicomponent, flow and reactive transport simulation capability for environmental applications. It includes toolsets for meshing infrastructure, discretizations, and solvers for the resulting nonlinear systems of equations. The code is parallel and makes use of open-source parallel frameworks such as Trilinos developed at Sandia National Laboratory and PETSc (the Portable Extensible Toolkit for Scientific Computing) developed at Argonne National Laboratory. Amanzi is used to model contaminant migration at various DOE waste sites (e.g., Hanford, and Savannah River), and is generally applicable to contaminant migration in groundwater/surfacewater under partially saturated, non-isothermal conditions and its interaction with surface water. Development of Amanzi is funded by the DOE Office of Environmental Management under the Advanced Simulation Capability for Environmental Management (ASCEM) program.