Lgraph is an interactive, graphical software package to create, modify, and reduce linear graphs. Linear graphing is a structured method to formulate and represent lumped-element, linear dynamic system models containing connected single-port energy storage, dissipative, and source elements and two-port transduction elements. Lgraph enables the user to place elements from several domains in a connected graph, and then computes and displays elemental equations, constraint (loop and node) equations, and state equations for the dynamic system, all in symbolic form. The package was implemented using X Windows graphics and runs on Unix-based engineering workstations. It is currently being used by undergraduate students in the Department of Mechanical Engineering at the Massachusetts Institute of Technology (M.I.T.).