HAZMATH: a simple finite element, graph and solver library. The HAZMATH Finite Element (FE) and Solver library is built from C (C99 compatible) source files and provides software components that can be used to simulate physical/social phenomena described by Partial Differential Equations (PDEs), systems of PDEs, or graphs. We have included several standard discretizations for PDEs, often used in various applications. Our examples range from simple scalar elliptic PDEs to systems of PDEs, include time-dependent and nonlinear problems, and contain methods for the solution of linear systems. Our aim is to provide a basic tool, which can be used to tackle specific problems on demand. We do not intend to create a universal package that contains all discretizations available. HAZMATH contains the software to solve numerical models based on finite-element/volume/difference discretizations, and our team can assist in tweaking and adjusting these basic tools to meet the demands of the specific application. Thus, we aim to complement the user’s expertise and help build application-specific packages.