PIFISS Software Package: Potential (Incompressible) Flow & Iterative Solver Software. This is an open-source MATLAB with FEMLAB software package. It is associated with the project ”Uncertainty quantification in computer simulations of groundwater flow problems with emphasis on contaminant transport.” The PIFISS software can be used to generate typical linear systems arising from deterministic finite element discretizations of two important PDE applications: (variable) diffusion and potential flow. Mesh generation is done using FEMLAB. For potential flow, discretization is with the lowest order Raviart-Thomas mixed approximation method. The package has built-in algebraic multigrid and Krylov subspace solvers and appropriate preconditioning strategies for each problem. PIFISS has been developed using Femlab 3.1 and Matlab Version 7.1 and it can be run under Windows, Unix and Mac architectures.