Enthalpies of solution for (fumaric acid + water) have been measured at the temperatures (298.15, 313.15, and 333.15) K over the composition range of homogeneous solutions by using a SETARAM C80 D mixing calorimeter. The concentration and temperature dependence of the molar enthalpies of solutions and excess molar enthalpies are given by a Redlich-Kister equation fitted to the experimental data. The standard enthalpy of solution was determined by considering the effect of incomplete dissociation of C4H4O4 on the solution data. Enthalpies of crystallization of fumaric acid in aqueous solutions have been measured at the temperatures (298.15, 303.15, 308.15, and 313.15) K during unseeded programmed crystallization. The molar enthalpies of crystallization data are thermodynamically consistent with those calculated from partial molar enthalpies of solution.